タフ

タフだなあ。

You're tough.

彼(かれ)はタフだから少しのことではへこたれない。

He won't be easily discouraged, because he's a tough guy.

見た目には優しそうだけど、彼(かれ)って皆から外柔内剛の結構なタフネゴシエータと言われているよ。

He seems like a softy on the surface, but at the core he's got an iron will that makes him an extremely tough negotiator.