Roman Catholic Church. a head-piece consisting of three coronets on top of which is an orb and a cross, worn by the pope, or carried before him during certain nonliturgical functions.
3.
the position, authority, and dignity of the pope.
4.
a high headdress, or turban, worn by the ancient Persians and others.
1555, "headdress of the Persian kings" (also worn by men of rank), from L. tiara, from Gk. tiara, of unknown origin. Earlier in Anglicized form tiar (1513).