The godmother of one's child, or the mother of one's godchild; (more generally) a term of affectionate respect for any female friend. Also (derogatory): an old woman, a gossip; an effeminate man.
1940s. From French Creole macoumèr from French ma commère, lit. ‘my child's godmother’, friendly mode of address to an older woman from ma my + commère.