A solution of formaldehyde gas dissolved in water, typically around 40% concentration, widely used as a disinfectant and preservative.
German trademark 'Formalin' from 'Formaldehyd' (formaldehyde) + suffix '-in', established in the late 1800s when the compound was first synthesized commercially. It became genericized across many languages.
Formalin was a medical revolution—before modern refrigeration, it allowed hospitals and museums to preserve specimens for decades. Your high school biology class's preserved specimens probably still contain the exact same formalin formula from the 1900s!
Complete word intelligence in one call. Free tier — 50 lookups/day.