The triad or three-in-one
A modern phonetic spelling of Trinity, referring to the Christian doctrine of the Holy Trinity. It signifies three persons in one God: the Father, the Son, and the Holy Spirit.
Less common today
Trinidy isn't in the latest US Top 1000. It last peaked at #2,098 in 2000.
US births per 5-year period, 1990βpresent (SSA data).