/ dʒem; NAmE / noun
1.
(also less frequent gem·stone / ˈdʒemstəʊn; NAmE -stoʊn/) a precious stone that has been cut and polished and is used in jewellery
SYN jewel , precious stone :
a crown studded with gems
2.
a person, place or thing that is especially good :
This picture is the gem (= the best) of the collection.
a gem of a place
She's a real gem!
—compare jewel
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WORD ORIGIN
Old English gim , from Latin gemma bud, jewel; influenced in Middle English by Old French gemme .