say it: dek
dec is a noun meaning "the last (12th) month of the year". It carries 2 recorded senses.
the last (12th) month of the year
(astronomy) the angular distance of a celestial body north or to the south of the celestial equator; expressed in degrees; used with right ascension to specify positions on the celestial sphere
astronomy
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 dec 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.