tetrahydrofolic acid

noun

tet·​ra·​hy·​dro·​fo·​lic acid -ˌfō-lik- 

: a metabolically active reduced form C₁₉H₂₃N₇O₆ of folic acid that acts as a coenzyme in the transfer of groups (as a methyl group) containing a single carbon atom in metabolic synthesis (as of purines)