formaldehyde /fɔː(ɹ)ˈmældɪhaɪd/ noun1 •The simplest aldehyde, HCHO, a colourless gas that has many industrial applications; it dissolves in water to give formol (10%) and formalin.The shark chosen to replace the original was injected with 224 gallons of formaldehyde, ten times the amount used on the first shark and in a stronger concentration. — 2010 formsformaldehydes