- a white, crystalline polymer of formaldehyde, (HCOH)n, from which it is obtained by evaporation of the aqueous solution: used chiefly as an antiseptic.
- a white amorphous solid polymeric form of formaldehyde: used as a convenient source of formaldehyde and as a fumigant. Formula: (CH 2 O) n, where n lies between 6 and 50
