par•a•form•al•de•hyde(par′ə fôr mal′də hīd′, -fər-),USA pronunciationn.[Chem.]a white, crystalline polymer of formaldehyde, (HCOH)n, from which it is obtained by evaporation of the aqueous solution: used chiefly as an antiseptic. Also called par•a•form(par′ə fôrm′).USA pronunciation