gem
noun [ C ] uk/dʒem/ us/dʒem/
(JEWEL)
(also gemstone)（尤指切割成规则形状的）宝石
a jewel (= precious stone), especially when cut into a particular regular shape
(VERY GOOD)
难能可贵的人（或物）;被人喜爱的人（或物）;非常有用的人（或物）
someone or something that is very good, pleasing, or useful
He's a real gem - you'd be a fool to break up with him. 他可真是个宝贝——你得是个傻瓜才会想要跟他分手。
The coffee house is a hidden gem (= something that not a lot of people know about). 这个咖啡馆真是块隐藏的瑰宝。