chief priest; resident priest
Specifically the head priest who resides at and oversees a Buddhist temple. Not a general term for any monk.
あの寺の住僧は、毎朝早くからお経をあげている。
The chief priest of that temple chants sutras early every morning.
住僧が交代してから、寺の雰囲気が変わった。
The atmosphere of the temple changed after the resident priest was replaced.
Compound of 住 (reside) and 僧 (monk/priest), literally 'residing priest'. The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning of a priest who lives at and manages a temple.