gemsmith
A maker or worker of gems; a jeweler
“And a lesser gemsmith would not pay nearly the diamonds' worth. In fact, the shabbier and shadier the operation, the less blunt Martin can expect.” Queenie and Hellen exchanged glances. They both know the shabbiest, shadiest fence of all.
Where it comes from
From gem + smith. Compare Old English gimwyrhta (“jeweler”, literally “gem-wright/gem-worker”).
Adapted from the Wiktionary entry gemsmith (CC BY-SA 4.0).