velum (n.)

c. 1200, "nun's head covering," from Anglo-French and Old North French veil (12c., Modern French voile) "a head-covering," also "a sail, a curtain," from Latin vela, plural of velum "sail, curtain, covering," from PIE root *weg- (1) "to weave a web." Vela was mistaken in Vulgar Latin for a feminine singular noun. To take the veil "become a nun" is attested from early 14c.