say it: HAHL-mahrk
hallmark is a noun meaning "a distinctive characteristic or attribute". It carries 2 recorded senses.
a distinctive characteristic or attribute
a mark on an article of trade to indicate its origin and authenticity
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 hallmark 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.