1) Quantum mechanic 
In physics, multiplet can mean: The best known example is a spin multiplet, which is a group representation of an SU(2) subgroup of the Lorentz algebra. For example, a spin singlet is a trivial representation, a spin doublet is a fundamental representation and a spin triplet is a vector representation. In other cases, the term multiplet usually re...
(from the article `chemical compound`) ...absorption peaks. In the bromoethane example, the CH3 peak is split into three distinct peaks, called a triplet. The CH2 peak is split into four ...
A group of spectral lines showing fine structure with several components caused by spin-orbit interactions in the atom.
a group of several related spectral lines, usually of nearly the same wavelengths. Also called