1. a pair of similar or identical things; a couple or duo.
Usage: less common than 'pair' or 'couple'; often used in technical or specialized contexts
2. in physics and chemistry, a pair of closely spaced spectral lines or energy levels.
Usage: technical; used in atomic and molecular spectroscopy

Examples

• The dancers performed as a duplet, moving in perfect synchronization.
• The spectroscope revealed a duplet in the emission spectrum of the element.
• A duplet of swans glided across the lake.
• In quantum mechanics, the energy duplet arises from spin-orbit coupling.
• The duplet of stars orbits around a common center of mass.