jewel

Concise Oxford English Dictionary © 2008 Oxford University Press:
jewel/ˈʤuːəl/

▶noun

• 1 a precious stone, especially a single crystal or a cut and polished piece of a lustrous or translucent mineral.

  ■ (jewels) pieces of jewellery.

  ■ a hard precious stone used as a bearing in a watch, compass, etc.

• 2 a highly valued person or thing.

– derivatives
jewelled (US jeweled) adjective.

– phrases
the jewel in the (or one's) crown the most valuable or successful part of something.

– origin ME: from OFr. joel, from jeu ‘game, play’, from L. jocus ‘jest’.