flask / flask/ • n. a container or bottle, in particular: ∎ a narrow-necked glass container, typically conical or spherical, used in a laboratory to hold reagents or samples. ∎ a metal container for storing a small amount of liquor, typically to be carried in one's pocket: his silver flask of brandy. ∎ a narrow-necked bulbous glass container, typically with a covering of wickerwork, for storing wine or oil. ∎ a small glass bottle for perfume. ∎ a vacuum flask. ∎ the contents of any of these containers: a flask of coffee. ∎ hist. short for powder flask.ORIGIN: Middle English (in the sense ‘cask’): from medieval Latin flasca. From the mid 16th cent. the word denoted a case of horn, leather, or metal for carrying gunpowder. The sense ‘glass container’ (late 17th cent.) was influenced by Italian fiasco, from medieval Latin flasco. Compare with flagon.