from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A long time, years and years.
from the GNU version of the Collaborative International Dictionary of English
- n. a very long time; ages.
1923, from donkey's ears, which is rhyming slang for years. That is, donkey's ears is rhyming slang, replacing years with ears, while donkey's years reverts back to years, with donkey acting as emphasis. “Donkey’s ears” implies “a long time” because donkey’s ears are long, while “donkey’s years” is supported by the belief that donkeys live a long time. (Wiktionary)