Here's a breakdown:
* Old English: The word "monkey" originally came from the Old English word "ape," which itself came from the Old French word "ape."
* Middle English: In Middle English, the spelling evolved to "monke."
* Modern English: The "e" was added to the end during the transition to Modern English. This was a common practice to indicate a long vowel sound.
Essentially, the "e" at the end of "monkeys" is a leftover from historical spelling conventions and has no effect on the pronunciation.