cusp
cusp / kəsp/ • n. 1. a pointed end where two curves meet, in particular: ∎ Archit. a projecting point between small arcs in Gothic tracery. ∎ a cone-shaped prominence on the surface of a tooth, esp. of a molar or premolar. ∎ Anat. a pocket or fold in the wall of the heart or a major blood vessel that fills and distends if the blood flows backward, so forming part of a valve. ∎ Math. a point at which the direction of a curve is abruptly reversed. ∎ each of the pointed ends of a crescent, esp. of the moon.2. Astrol. the initial point of an astrological sign or house: he was Aries on the cusp with Taurus. ∎ fig. a point between two different situations or states, when a person or thing is poised between the two: those on the cusp of adulthood.DERIVATIVES: cus·pate / ˈkəspət; -ˌpāt/ adj.cusped adj.cus·pi·date / ˈkəspəˌdāt/ adj.
