doublet
Pronunciation: /ˈdʌblɪt/
noun
- 1a pair of similar things, in particular two words of the same derivation but having different meanings, for example fashion and faction, cloak and clock.
- (doublets) the same number on two dice thrown at once.
- Physics & Chemistry a pair of associated lines close together in a spectrum or electrophoretic gel.
- a combination of two simple lenses.

Origin:
Middle English: from Old French, 'something folded', also denoting a fur-lined coat, from double 'double'