To follow up on FumbleFingers's OED quote, I note that the "to look over or through in a casual or cursory manner" definition is a relatively recent addition to the Merriam-Webster's entry for peruse. That definition first appears (in the Collegiate series) in the Tenth Collegiate Dictionary (1993). The Ninth Collegiate Dictionary (1983) has a substantially shorter entry for peruse:
1: to examine or consider with attention and in detail: STUDY 2: READ
Perhaps the most ambiguous definition of peruse in the Tenth Collegiate Dictionary is the revised form of the older definition 2 ("READ"):
2: READ; esp., to read over in an attentive or leisurely manner
This definition remains unchanged in the Eleventh Collegiate Dictionary (2003), still the most recent edition in the Collegiate Series. To me, "an attentive or leisurely manner" is a bit like "a hard-working or indolent manner"—it covers a lot of ground in two places with very little overlap between them.
Because the word can mean quite different things nowadays, I wouldn't assign a more specific meaning than "read" to any contemporary occurrence of it unless I had contextual clues to help me interpret the speaker's (or writer's) intent.
FOLLOW-UP: Various grammar and usage commentators have addressed the proper usage of peruse. For example, Eric Partridge, Usage and Abusage, Fifth Edition (1957) offers this entry:
peruse is not synonymous with 'to read', for it means to read thoroughly, read carefully, from beginning to end. One peruses a contract, one reads an (ordinary) advertisement—that is, if one does not merely glance at it.
Bryan A. Garner, Modern American Usage (2003) expresses a similar view:
peruse (= to read with great care) is pompous and stilted in business correspondence. That is, the word shouldn't be used merely as a fancy substitute for read. ... Some writers misuse the word as if it meant "to read quickly" or "scan" [examples omitted]. That slipshod extension has become common enough to be listed in some dictionaries. But since it's the opposite of the word's traditional meaning, that usage is best shunned.
Of course, both Partridge and Garner focus on how peruse should be used, not on how people actually use it. For a descriptivist view—and a critique of prescriptivist hostility toward using peruse to mean simply "read"—we can consult Webster's Dictionary of English Usage (1989). Its discussion runs for a page and a half.
Briefly, WDEU argues that peruse arose as "a literary word" that, in poetry, served as "a useful alternative to the monosyllabic read." WDEU traces hostility to the use of peruse to mean simply "read" to Frank Vizetelly, A Desk-Book of Errors in English (1906), which made the following assertion:
peruse should not be used when the simple read is meant. The former implies to read with care and attention and is almost synonymous with scan, which is to examine with critical care and in detail. A person is more apt to read than to scan or peruse the Bible.
Incidentally, scan has long since completed the bipolar metamorphosis that some people now attribute to peruse. As Garner notes, "scan is ambiguous: it may mean either (1) 'to examine carefully, scrutinize' or (2) 'to skim through, look at hurriedly.' In [American English], as it happens, sense 2 now vastly predominates—a tendency bolstered by the ubiquitous electronic scanner, which contribute to the idea of haste."
According to WDEU, "it appears that this notion of the correct use of peruse was Vizetelly's own invention. It was certainly born in disregard of dictionary definitions of the word and in apparent ignorance of the literary traditions on which those dictionary definitions were based."
WDEU then cites 21 examples (ranging in publication date from 1594 to 1968) involving peruse—some with a narrowing adverb such as thoroughly, diligently, or attentively, or (contrariwise) negligently or idly, and others with no adverbial modifiers (such as "I perused a number of public notices attached to the wall," from a 1939 book by Flann O'Brien). Then it makes its central argument:
You may have noticed by now that the plain word read can readily be substituted in any of these examples, even where the idea of "read through or over" is pretty obvious.
...
In conclusion we recommend that you reread the examples and see for yourself in how many Samuel Johnson's simple "read" definition would work perfectly well. There are likely to be only a few in which adding the adverbs used by later dictionary definers will enhance anyone's understanding of the passage.
Under the circumstances, I don't think that the Tenth Collegiate's 1993 expansion of the second definition of peruse four years after WDEU appeared from "READ" to "READ; esp., to read over in an attentive or leisurely manner" represents a disavowal by Merriam-Webster's of the generic sense "read" in favor of something along the lines of "either read in an attentive manner or read in a leisurely manner, but not simply read." Rather, I think it reflects Merriam-Webster's desire to call out the two most common narrower senses that peruse-as-"read" takes, while upholding the continued validity of the root meaning "read."
In any event, Merriam-Webster's republished WDEU as Merriam-Webster's Dictionary of English Usage in 1994 (one year after the Tenth Collegiate appeared) with its lengthy discussion of peruse unchanged.
Best Answer
For historical context, here are the entries for quixotic that appear in Merriam-Webster's Collegiate Dictionary series, from the first edition (1898) through the eleventh (2003).
Webster's Collegiate Dictionary, first edition (1898):
Webster's Collegiate Dictionary, second edition (1910):
Webster's Collegiate Dictionary, third edition (1916):
Webster's Collegiate Dictionary, fourth edition (1931):
Webster's Collegiate Dictionary, fifth edition (1936):
Webster's Collegiate Dictionary, sixth edition (1949):
Webster's Collegiate Dictionary, seventh edition (1963):
Webster's Collegiate Dictionary, eighth edition (1973):
Merriam-Webster's Collegiate Dictionary, ninth edition (1983):
Merriam-Webster's Collegiate Dictionary, tenth edition (1993):
Merriam-Webster's Collegiate Dictionary, eleventh edition (2003):
Over the years, various minor changes in the Collegiates' handling of quixotic are evident. For example, in 1916, the dictionary dropped the wording "apt to be deluded" from the earlier definition; and in 1931, the dictionary replaced the disapproving language about extravagance and absurdly chivalric behavior in the entry for quixotic with the simpler and more neutral wording "idealistic but unpractical."
But bigger changes occurred in 1963, when, for the first time, the dictionary dropped the explicit association of the word quixotic with the character and behavior of the fictional character Don Quixote; and in 1983, when, out of nowhere, the dictionary introduced "capricious and unpredictable" as a second definition of the word.
I don't know what prompted the lexicographers at Merriam-Webster to introduce this second definition, but presumably they were persuaded that usage of the word in that sense was so widespread and firmly established to they could not in good descriptivist conscience ignore it.
When I read or hear someone using the word quixotic, my immediate reaction is to apply the characteristics of Don Quixote to the relevant context Those characteristics include chivalrousness, honor, impracticality, delusion, and steadfast devotion to a cause or quest.
This last characteristic is rather severely at odds with the attributes of capriciousness and unpredictability suggested by the new, second definition in the Ninth Collegiate; and I have to think that that conflicting meaning arose because people who had never read the book imagined that seeing windmills as giants (for example)—or believing a not very virtuous barmaid to be an almost saintly embodiment of feminine virtue—was an instance of capriciousness and unpredictability. In fact, as presented within the novel, they are signs of delusional thinking that is anything but inconsistent or capricious; perhaps the main poignancy of the novel lies in Don Quixote's virtuous fidelity to his duty, as he understands it, given his delusions.
But in the real world, people are not required to read (much less appreciate) Don Quixote before using the word quixotic. And it is hardly surprising that—in a society whose members are less and less familiar with literary classics from the ancient days before there was an Internet—words that originated as allusions to specific books and even to specific characters lose their mooring in popular culture and begin to be used in ways that are not at all true to their source.