D defs.my
Entry 1 sense Webster, 1913

Pendentive

/(pĕn*dĕnt"ĭv)/ · Pen·den·tive · IPA
01 n. The portion of a vault by means of which the square space in the middle of a building is brought to an octagon or circle to receive a cupola.
  1. 1.
    The portion of a vault by means of which the square space in the middle of a building is brought to an octagon or circle to receive a cupola.(Arch.)