It was very generous of him to pay for all our lunches.

generous 是形容词，意思是"慷慨的、大方的"，形容一个人乐于给予或分享，不计较付出多少。这个词来自拉丁语词根 generosus，原意是"出身高贵的"，后来引申为"品格高尚、慷慨大方"的意思。