From Longman Dictionary of Contemporary Englishdonkey’s yearsdonkey’s yearsLONG TIME British English spoken a very long timefor donkey’s years I’ve had this jacket for donkey’s years. → donkey
Examples from the Corpus
donkey’s years• She worked in the shop for donkey's years, although the pay was awful.• It's donkey's years since I went to the movies.• We used to play golf together, but that was donkey's years ago. 