1.
US
a weak or servile man (often used as a contemptuous term for a man with moderate or progressive political views).
"we act like a bunch of cucks who let them take what they want"
2.
a man whose wife is sexually unfaithful; a cuckold.
verb
make (a man) a cuckold by having a sexual relationship with his wife or by being sexually unfaithful to him.