say it: ep-i-THEE-lyuhm
epithelium is a noun meaning "membranous tissue covering internal organs and other internal surfaces of the body". It carries one recorded sense.
membranous tissue covering internal organs and other internal surfaces of the body
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 epithelium 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.