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1. A spectral line having more than one component, representing slight variations in the energy states characteristic of an atom.
2. Any group of subatomic particles that are similar in most properties, but have different electric charges, such as the nucleons, which form a doublet, or the pions, which form a triplet.
1. (General Physics) a set of closely spaced lines in a spectrum, resulting from small differences between the energy levels of atoms or molecules
2. (General Physics) a group of related elementary particles that differ only in electric charge
[from multiple; on the model of doublet]