Why is the ninth month called September?
early 15c., "seizing property or citizens of another nation in retaliation for loss inflicted on one's own," from Anglo-French reprisaille (14c.), from Old French reprisaille (Modern French représaille), from early Italian ripresaglia, from ripreso, past participle of riprendere "take back," from Latin reprendere, earlier reprehendere (see reprehend). General sense of "retaliation" is from 1710.
An act by which a nation seeks, short of war, to redress a wrong committed against it by another nation. Boycotts and blockades are common forms of reprisal.