wittol

n. Archaic
A man who knows of and tolerates his wife's infidelity.

[Middle English wetewold : weten, to know (from Old English witan; see wit²) + (coke)wold, cuckold; see cuckold.]

1) a husband who accepts his wife's infidelity
2) a stupid person; a person with no wits, not even a half-wit