FLASK, in its earliest meaning in Old English a vessel for carrying liquor, made of wood or leather. The principal applications in current usage are (1) to a vessel of metal or wood, formerly of horn, used for carrying gunpowder; (2) to a long-necked, round-bodied glass vessel, usually covered with plaited straw or maize leaves, containing olive or other oil or Italian wines - it is often known as a "Florence flask": similarly shaped vessels are used for experiments, etc., in a laboratory; (3) to a small metal or glass receptacle for spirits, wine or other liquor, of a size and shape to fit into a pocket or holster, usually covered with leather, basket-work or other protecting substance, and with a detachable portion of the case shaped to form a cup. "Flask" is also used in metal-founding of a wooden frame or case to contain part of the mould. The word "flagon," which is by derivation a doublet of "flask," is usually applied to a larger type of vessel for holding liquor, more particularly to a type of wine-bottle with a short neck and circular body with flattened sides. The word is also used of a jug-shaped vessel with a handle, spout and lid, into which wine may be decanted from the bottle for use at table, and of a similarly shaped vessel to contain the Eucharistic wine till it is poured into the chalice. "Flask" (in O. Eng. flasce or flaxe) is represented both in Teutonic and Romanic languages. The earliest examples are found in Med. Lat. flasco, flasconis, whence come Ital. fiascone, O. Fr. flascon (mod. flacon), adapted in the Eng. "flagon." Another Lat. form is flasca, this gave a Fr. flasque, which in the sense of "powder flask" remained in use till later than the 16th century. In Teutonic languages the word, in its various forms, is the common one for "bottle," so in Ger. Flasche, Dutch flesch, etc. If the word is of Romanic origin it is probably a metathesized form of the Lat. vasculum, diminutive of vas, vessel. There is no very satisfactory etymology if the word is of Teutonic origin; the New English Dictionary considers a connexion with "flat" probable phonetically, but finds no evidence that the word was used originally for a flat-shaped vessel.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)