overflown

From over- +‎ flown.

overflown

1. past participle of overfly

From Middle English overflowen (past participle of overflowen besides rare overflowed), from Old English oferflōwen (past participle of oferflōwan).

overflown

1. (US, proscribed) past participle of overflow

The use of the past participle overflown for overflow sometimes occurs in American English, where it is often proscribed and seen as resulting from a confusion of overflow and overfly. However, it was once more prevalent throughout the English-speaking world, and is ultimately the original form.