define precursor
Meaning of âprecursorâ in the English Dictionary. See all translations. uk â /ËpriËËkÉË.sÉr/ us â /ËpriËËkÉË.sÉ/ formal. âº something that happened or existed before another thing, especially if it either developed into it or had an influence on it: Sulphur dioxide is the main precursor of acid rain. Biological research has often been a precursor to medical breakthroughs.