the union of the Father and Son and Holy Ghost in one Godhead
"The doctrine of the trinity teaches that the Father, Son, and Holy Ghost are united as one Godhead."
A group or set of three people or things; three things combined into one.
"The trinity of classical gods in ancient Rome consisted of Jupiter, Mars, and Quirinus."
In plain English: A trinity is a group of three things that are considered to be one single unit, often used by Christians to describe God as Father, Son, and Holy Spirit all being the same deity.
"In Christian tradition, God is often referred to as the trinity consisting of the Father, Son, and Holy Spirit."
Usage: Use trinity to describe any trio where the three elements are closely linked, such as in religious contexts or natural phenomena like a rainbow's colors. Avoid using it for unrelated groups of three items that simply happen to be counted together.
In Christian belief, the three persons (personae) of the Godhead: Father, Son and Holy Spirit.
"According to traditional Christian doctrine, the Trinity consists of the Father, the Son, and the Holy Spirit as one divine being."
The word "trinity" comes from the Latin trinitas, meaning a state of being three, which entered Middle English through Anglo-Norman and Old French. It replaced an earlier native Old English term that literally meant "threeness."