A man who lets his wife or girlfriend have sex with other men. Often the man lets her do whatever she wants and treat him like shit.
(Short version of cuckold)

A man who is desperate for acceptance, approval, and affection from women. This desperation has led to the compromise of his beliefs and values, the desecration of his dignity and self-worth, and his inability to stand up for himself and what he deserves as a human being, eg. loyalty, fidelity, and honesty in a romantic relationship.

Cuck is a man who's a little bitch. Contrary to the beliefs of the liberal leaning crowd trying to explain something popularized by the conservatives, cuck is used by many races for someone who is spineless and IS derived from cuckold.

a cuck is a husband that lets his wife fuck other people and finds enjoyment in this

Short for cuckold

A person (usually a man) who lets others (usually women) metaphorically walk all over them in the name of "being a better person", or as a fetish.

short verb form for cuckold, to make your spouse a cuckold.

:Based on the sexual term cuckold, a cuck is a politician that chooses to represent large donating special interest groups rather than the voting majority. In essence the politician watches and allows a narrow view special interest to take advantage of the public interest. This nickname has been a phenomenon that emerged as part of the 2016 primary election regarding establishment politicians.