Learn English – Could the term “elephant” have derived from “olfactory?”

Early on that word of course was used to talk about the action of cleaning something off with a garden hose, but that is not the meaning you are asking about. I do not recall ever hearing that term used with that meaning before the 80's. What happened in the 80's?

Well, SCTV had a very funny (to us USAsians) skit with a couple of stereotypical Canadians called the McKenzie Brothers. They were constantly calling each other "hosers", and talking about how they had "hosed" each other. The skit went the 80's equivalent of viral, with an album (with a couple of singles that got good airplay) and a movie spun off it. The effect was that we (in the USA) got "hoser" added to the language as sort of a good-natured insult, or a way to make fun of Canadian speech.

Along with it, we borrowed the verb and adverb forms of "hosed" from the same source. Its a much more useful word, so it kinda lost its association with Canadians, and got fully adopted into the USA lexicon.

So where did Canadians come up with these words? That's where personal experience fails me, so I have to rely on online sources:

Like the very similar term hosehead, the term may have referred to farmers of the Canadian prairies, who would siphon gas from farming vehicles with a hose during the Great Depression of the 1930s.[citation needed] The expression has since been converted to the verb 'to hose' as in to trick, deceive, or steal - for example: "That card-shark sure hosed me." Hosed has an additional meaning of becoming drunk - for example: "Let's go out and get hosed." Another possible origin is derived from hockey slang. Before ice resurfacers, the losing team in a hockey game would have to hose down the rink after a game. Thus the term "hoser" being synonymous with "loser".

Personally I prefer the hockey explanation, but that doesn't make it right.

Currently the OED says there is no clear evidence of the term being used prior to its use by Rick Moranis and Dave Thomas, which to my mind leaves a strong possibility that they may have invented the slang themselves (although they are both Canadian, so they could well just be the first to record an existing slang).

The two earliest instances of preplan/preplanned/preplanning (with or without a hyphen) that a Google Books search finds are from the pen of Robert Southey, who was Poet Laureate of England for the last thirty years of his life (from 1813 to 1843). The first instance is from a letter by Robert Southey to the Reverend Neville White, dated February 19, 1824, reprinted in Selections from the Letters of Robert Southey (1856):

My dear Neville,

Here I am, once more at my desk, by my own fire-side. My movements were all punctually performed, as they had been pre-planned. I reached home on Sunday morning, without impediment or mishap of any kind, and, thank God, found all well. Some little time is required before I can fairly get into joint again, after so complete a dislocation ; and I bring back with me a formidable accumulation of letters, which followed and found me whithersoever I went, and which it was not possible for me to answer during so hurried a mode of life.

The next is a quotation from Robert Southey's "Colloquies on the Progress and Prospects of Society," in a review of that work in Blackwood's Edinburgh Magazine (October 1829):

Montesinos [a character in Southey's dialogue, speaking to Thomas More]. Like the whole fabric of our society, it [the manufacturing system in contemporaneous England] has been the growth of circumstances, not a system pre-planned, foreseen, and diliberately chosen. Such as it is, we have inherited it, or rather have fallen into it, and must get out of it as well as we can. We must do our best to remove its evils, and to mitigate them while they last, and to modify and reduce it till only so much remains as is indispensable for the general good.

From "Shakespeare in Modern Thought," in North American Review (October 1857):

The events and characters of a drama may be very amusing and interesting, may be morally and spiritually edifying ; but unless they proceed from some common point of view, some pervading, centralizing principle, and so are related essentially to one another, having a common life, they do not belong to the domain of rt. There is undoubtedly, such a universal "central idea" for each living man. The dramatic poet, like a presiding deity, surveys all the details, and holds in his hands the threads of connection and relation, so that his representation is no patchwork of circumstances and capricious succession of words and deeds, but a regular and pre-planned figure, woven out of many different and variously colored threads, each of which has its place in the finished product, and is essential to a complete embodiment of the ideal pattern.

From "Long Vacation," in London Society (January 1868):

Then came preparation, packing, and departure. One by one the crew broke away ; cordially we shook hands, and pre-planned réunions in town, at Lord's, in the Highlands, and elsewhere.

From John Scott Russell, Systematic Technical Education for the English People (1869) [the same year as the New York Court of Appeals Decision cited in bib's answer]:

But the growing youth, who has everything to learn, and no help, how is he to find fit education and training for his work in life? For the ordinary English lad, education must be pre-planned, prepared, brought home to him, to his father's home, to his master's workshop. He cannot seek education. We must seek him.

The origin of the word preplan thus appears to rest not with an anonymous twentieth-century purveyor of business jargon, but with a nineteenth-century poet and litterateur; and other early instances of the phrase show its being taken up in the fields of literary criticism, memoir, pedagogy, and law. The modern notion of convening a preplanning meeting before the planning meeting to work out what will be covered and (perhaps) decided at the latter may be a creature of corporate or government bureaucracy; but preplanning itself evidently was not born in a conference room.

With a confirmed first occurrence Google Books search results of 1824, preplan actually beats the earliest confirmed match for the phrase "plan ahead"—which has its own problem with face-value redundancy, and which has a confirmed first occurrence of 1848 in Google Books search results. I see very little change in the sense of preplanned from its meaning as used by Southey in the 1820s and its meaning as given by Oxford and Collins and quoted in Mari-Lou A's question.