Merriam-Webster's Collegiate® Dictionary, 11th Edition
TRINITY
I. noun
Etymology: Middle English trinite, from Anglo-French trinité, from Late Latin trinitat-, trinitas state of being threefold, from Latin trinus threefold
Date: 13th century
the unity of Father, Son, and Holy Spirit as three persons in one Godhead according to Christian dogma, a group of three closely related persons or things, the Sunday after Whitsunday observed as a feast in honor of the trinity,
II. geographical name river E Texas flowing SE into Galveston Bay