also: がたいがよい
expression, i-adjective (yoi/ii class)
big and brawny; well-built; gigantic
Describes a person, especially a man, with a large, muscular, or imposing physique. Often carries a nuance of rough strength. Used in casual conversation.
あの俳優はガタイが良くて、アクションシーンが映える。
That actor is big and brawny, so his action scenes look great.
兄はガタイがいいから、力仕事は任せている。
My older brother is well-built, so I leave the heavy lifting to him.
The word ガタイ is a colloquial term for a person's build or frame, likely derived from 体 (からだ) with a sound shift. The exact origin is uncertain, but it is used almost exclusively in the phrase ガタイが良い/いい.