the.com/trinity

means A group of three closely connected people or things regarded as one unit — most specifically, in Christian theology, the union of Father, Son, and Holy Spirit as a single Godhead.

from From Latin 'trinitas,' meaning 'threeness' or 'triad,' built from 'trini' ('three each') — itself related to 'tres,' the ordinary Latin word for three. Early Christian writers coined 'trinitas' to name a doctrine the word 'three' alone couldn't carry, and it passed into English through Old French 'trinité' around the 1200s. The theological sense came first; the word only later loosened up to describe any cozy threesome of things — ideas, people, Lego sets — united in spirit if not in substance.