say it: SING-guhl-tuhn
singleton is a noun meaning "a single object (as distinguished from a pair)". It carries 3 recorded senses.
a set containing a single member
the playing card that is the only card in a suit held in a bridge hand as initially dealt
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for singleton come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.