The origin of this name is unknown :

Possibility No 1 (Tre) (Glamus) – Sector of Glamus. Glamus was an Irish monk who came to Brittany with the goal of Christianising it. An English tourist has claimed that there was another Treglamus in Wales….but this has not been confirmed.

Possibility No 2 is less convincing.
Tre-glanviz ….spot favourable to illnesses

Possibility No 3 – deformation of the word Trefflamus (sector of St Efflam) Treglamus was a sub-division of the parish of Pedernec. It became a parish in its own right following the Revolution. Its first rector in 1800 was a M. Connan