Interesting. Later I'll rewind the presentation we were watching to make sure what exactly the host said.Incidentally, although "for" appears to be required grammatically with "donkey's years", it is usually omitted, in my experience. Most other similar expressions generally include "for".
No. See post 10 and also the OEDMy understanding is that donkey's ears originated as cockney rhyming slang.
donkey's years n. (also donkeys' years (occasionally donkeys' ears with punning allusion to the length of a donkey's ears and to the pronunciation of ears as years)) colloquial a very long time.
This is all very hypothetical. Without substantial evidence, I am disinclined to believe it.I don't see any reason why it should not have come from rhyming slang, although it has mutated along the way.
The rhyming slang would, of course, have been
years = donkey's earsThis fits the usual pattern of rhyming slang, except that the last word ("ears") is rather closer in sound to the word it represents ("years") than is usual. As with most examples of rhyming slang, it would not have made it into print very often.
Following the usual pattern of rhyming slang, we might expect "donkey's ears" to be shortened to "donkey's", and we do in fact see this. Examples are hard to find because it is a difficult thing to search for, but this card (Haven't Seen Ewe In Donkeys Greeting Card by Artist Thomas Joseph) would make no sense if "donkey's" on its own wasn't a recognisable usage. Certainly I am familiar enough with "donkey's" on its own.
Somewhere along the line, though, "donkey's ears"/"donkey's" changed to "donkey's years".
If it does come from rhyming slang, then "donkey's ears" being long and "donkey's ears" referring to a long time appears to be a coincidence. There is usually no connection between the rhyme and what it represents.