early 15c., "quality of being straight," from Middle French rectitude (14c.), from Late Latin rectitudinem (nominative rectitudo) "straightness, uprightness," from Latin rectus "straight" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line"). Sense of "upright in conduct or character" is from 1530s.
rectangular
rectification
rectifier
rectify
rectilinear
rectitude
recto-
recto
rector
rectory
rectum