A colorless, aromatic, flammable liquid chemical derived from coal and petroleum; used as a solvent, fuel, and in manufacturing synthetic resins and pesticides.

First of the ten Heavenly Stems; used to indicate the first position in a sequence or rank, often equivalent to "A" or "I" in English lists; ancient Chinese compass point (75°)

(bound form) any of a class of organic compounds containing a carbonyl group with a single hydrogen atom; common examples include 甲醛 jiǎ​quán and 乙醛 yǐ​quán