One who let's his wife lay with other men without objection. (Italian)
One who allows the "horns" be put to him.
(Italian)
Same as "cabron" (Spanish)

One who let's his wife lay with other men without objection, or worse, without his knowledge. (Spanish & Italian)
One who allows the "horns" be put to him. (Spanish & Italian)
aka Cockold in old english

Avoid using this insult - it's a bad one.
You will get a violent response from all but the biggest cowards!