1911 Encyclopædia Britannica/Loop

LOOP. (1) A curve or bend, particularly a bend in a string, rope, &c., formed by doubling back one part so as to leave an opening; similarly a ring of metal or other material leaving an aperture. (2) In architecture or fortification, “loop,” more usually in the form “loophole,” is an opening in the wall of a building, very narrow on the outside and splayed within, from which arrows or darts might be discharged on an enemy, or through which light might be admitted. They are often in the form of a cross, and generally have round holes at the ends (see Oillets). (3) The word is also a term in iron and steel manufacturing for a mass of metal ready for hammering or rolling, a “bloom.”

This last word is represented in French by loupe, from which it is probably adapted. The earlier English form was also loupe, and it was also applied to precious stones which were of inferior brilliancy; the same also appears in French. Of the word in its two first meanings, a bend or circle in a line of string, metal, rails, &c., and “loophole,” the derivation is uncertain. Skeat takes the word in both meanings to be the same and to be of Scandinavian origin, the old Norwegian hlaup, a leap, being the direct source. The base is the Teutonic hlaufan, to run, to leap, German laufen. The New English Dictionary considers the Swedish example, löp-knut, “running knot,” and others given by Skeat in support of his derivation to be Germanisms, and also that the pronunciation of the word would have been lowp rather than lūp. “Loop” in meaning (2) “loophole” is also taken to be a different word, and is derived from Dutch luipen, to peer, watch. In modern Dutch the word for a narrow opening is gluip.