- cusp (n.)
- 1580s, from Latin cuspis "point, spear, pointed end, head," which is of unknown origin. Astrological use is earliest.
- cuspid (n.)
- 1743, from Latin cuspis (genitive cuspidus) "point, pointed end" (see cusp). Of teeth, from 1878. Related: Cuspidate (adj.), attested from 1690s.
- tricuspid (n.)
- 1660s, from Latin tricuspidem (nominative tricuspis) "three-pointed," from tri- (see tri-) + cuspis "point" (see cusp).