OED defines them as:
nonchalant adjective (of a person or manner) feeling or appearing casually calm and relaxed; not displaying anxiety, interest, or enthusiasm
insouciant adjective showing a casual lack of concern; indifferent
blithe adjective showing a casual and cheerful indifference considered to be callous or improper:
a blithe disregard for the rules of the road;
happy or joyous: a blithe seaside comedy
So, what would be the difference between say, "a nonchalant shrug" and
"an insouciant shrug"?
Also, what context are these words used in the following sentence:
"I would live all my life in nonchalance and insouciance Were it not
for making a living, which is rather a nouciance." Ogden Nash, poet
(Hard Lines, 1931)
Also, what does 'nouciance' mean? Is it simply a play on words?
Last, but most important, what word would best fit the following situation:
He was (nonchalant/insouciant/blithe) about the poor living conditions of the animals in his farm.
Best Answer
Some background on the difference between 'nonchalant' and 'insouciant'
Before focusing on the meanings of the two words, let's take a look at the Ngram chart for nonchalant (blue line) versus insouciant (red line):
According to Merriam-Webster's Eleventh Collegiate Dictionary, nonchalant entered English (directly from French) circa 1734, whereas insouciance—the noun form of insouciant—arrived (also directly from French) in 1799. The Ngram chart suggests that nonchalant has been several times more common than insouciant in published English texts for the past 150 years or so. Even so, I was somewhat surprised that the Eleventh Collegiate doesn't give insouciant a separate entry. Here are its entries for nonchalance and nonchalant:
And here is its entry for insouciance:
The synonyms note under the entry for cool discusses a group of similar adjectives: cool, composed, collected, unruffled, imperturbable, and nonchalant. Considering that MW views insouciance as meaning "lighthearted unconcern: NONCHALANCE," The exclusion of insouciant from the cluster of synonyms allied with cool is surprising and disappointing. The note on nonchalant in the entry under cool reads as follows:
This very much of a piece with the discussion of nonchalant in Webster's Dictionary of Synonyms (1942):
Meriam-Webster's Dictionary of Synonyms (1984) repeats its 42-year-older predecessor's entry almost word for word, except tht it drops the phrase "rather than necessarily implies" and replaces the T.E. Brown quotation with this one:
And yet the entry for nonchalant in Webster's Fifth Collegiate Dictionary (1936/1941) is quite different from the one that appears in Webster's Ninth Collegiate Dictionary (1983), which is identical to the entry (noted above) in the Eleventh Collegiate. Here is the Fifth Collegiate's entry:
nonchalant, adj. ... Lacking in warmth of feeling, enthusiasm, or interest; indifferent; also, Colloq[uial], casual and imperturbable.
The Fifth Collegiate's entry for insouciance, meanwhile, contains this information:
In effect, such difference as remains between nonchalant and insouciant in 1941 seems to reflect the difference in their French roots—nonchalance suggesting indifference through a lack of warmth or concern, and insouciance suggesting indifference through an absence of care or troubledness. The meanings are clearly very close, in any case.
One reference work that does provide discussions of both nonchalant and insouciant is S.I. Hayakawa, Choose the Right Word: A Modern Guide to Synonyms (1968). But rather unexpectedly, Hayakawa assigns the two words to different synonym groups: nonchalant lands in a group headed by flippant; and insouciant falls into group under jaunty.
Here are the relevant comments from these two discussions:
Here again, the distinction between the two words seems to rest primarily on a perceived difference between lack of concern (nonchalant) and lack of care (insouciant). Hayakawa seems to think that the former reflects an attitude while the latter reflects a spirit; I'm not at all persuaded that he is right.
My answers to the poster's specific questions
With regard to the poster's specific questions, I offer these answers:
1. To judge from the foregoing discussions of the meanings of insouciant and nonchalant, the difference between "a nonchalant shrug" and "an insouciant shrug" might be imperceptible to an objective viewer, although we might expect the insouciant shrug to be a bit more vigorous (because it expresses a carefree attitude) than the nonchalant shrug (which is likely to be muted by the shrugger's lack of concern for whatever has prompted the shrug.
2. Ogden Nash seems to be using the words nonchalance and insouciance without a great deal of regard for their overlap in meaning. He is aiming for comic effect and so is happy to use two words where one would convey the essential notion of cucumberish imperturbability.
3. Nash uses nouciance as a ludicrous spelling for nuisance, nothing more. A similar joke spelling for the sake of a rhyme appears in his famous short poem, "If called by a panther/ Don't anther."
4. As for the sentence "He was (nonchalant/insouciant/blithe) about the poor living conditions of the animals in his farm," I wholeheartedly agree with Edwin Ashworth's comment (beneath the question) that none of the three named options is as suitable as indifferent would be and that a change in preposition from about to to would further improve the sentence:
In my view, indifferent indicates a level of coldness toward potential suffering that the other terms—with their emphasis on disposition (blithe), attitude (nonchalant), or spirit (insouciant)—are ill equipped to convey.