say it: pree-KUR-sur
precursor is a noun meaning "a substance from which another substance is formed (especially by a metabolic reaction)". It carries 3 recorded senses.
a substance from which another substance is formed (especially by a metabolic reaction)
biochemistry
a person who goes before or announces the coming of another
something that precedes and indicates the approach of something or someone
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 precursor 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.