say it: uhn-MEN-shuh-nuh-buhl
unmentionable is a noun and adjective meaning "a garment worn under other garments". It carries 2 recorded senses.
a garment worn under other garments
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 unmentionable 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.