marry-in noun 2marry in verb 2forms 4 noun2 •A person who is on a family tree because he has married someone on the tree, and is not related by blood to anyone on the tree except his own descendants. •A protest where many people marry, as in protest of a law that forbids such marriages. marry in verb2 •To join a family or group through marriage.Marriage patterns were likely exogamous to the band, with women marrying in as wives, and with daughters and sisters marrying out. — 1998 •To marry someone of the same religious or ethnic group.The single ancestry women have a 9 to 5 ratio of marrying in to marrying out; those of a mixed ancestry have a 5 to 8 ratio. — 1976 formsmarried in · marrying in · marries in · marry-ins