a colorless poisonous gas; made by the oxidation of methanol
"The safety officer tested the air vents to ensure no trace of formaldehyde, that colorless gas formed during the methanol oxidation process, was leaking into the new classroom."
The simplest aldehyde, HCHO, a colourless gas that has many industrial applications; it dissolves in water to give formol (10%) and formalin.
"The factory workers had to wear special masks because leaking pipes were releasing toxic formaldehyde into the air."