"瘦" 的英语是 "thin"，来源是古英语中的 "þinn"，意思是身体瘦小，体重轻。

"强壮" 的英语是 "strong"，来源是古英语中的 "streng"，意思是身体健康，体格强健。

下面是一些英文例句及其中文翻译：

She's very thin, but she's also very fit. 她很瘦，但也很健康。
He's thin, but he's also very strong. 他很瘦，但也很强壮。
She's thin and depcate, but she's also very strong-willed. 她身材苗条，但意志坚强。
He's thin, but he's also very muscular. 他身材瘦弱，但肌肉发达。
She's thin, but she's also very healthy. 她身材苗条，但身体健康。