金龟 literally means 'golden tortoise,' but it's not the everyday word for tortoise (that's 乌龟). Historically, it refers to a golden tortoise emblem worn by Tang Dynasty officials as a badge of rank. In modern Chinese, you mostly encounter 金龟 in the idiom 金龟婿 (jīn guī xù), meaning 'ideal wealthy husband' — a cultural reference to a 'golden turtle son-in-law'. The word itself is rare outside this idiom.