What is Allonge?

Legal Definition
An allonge (from French allonger, "to draw out") is a slip of paper affixed to a negotiable instrument, as a bill of exchange, for the purpose of receiving additional endorsements for which there may not be sufficient space on the bill itself. An endorsement written on the allonge is deemed to be written on the bill itself. An allonge is more usually met with in those countries where the Code Napoleon is in force, as the code requires every endorsement to express the consideration. Under English law, as the simple signature of the endorser on the bill, without additional words, is sufficient to operate as a negotiation, an allonge is seldom necessary.

In fencing, an allonge is a thrust or pass at the enemy.

An allonge can also refer to a long (drawn out) espresso shot, also known as an Italian lungo.

In chemistry an allonge is an old French term for a separatory column.

In dressage an allonge is a long rein used for trotting a horse.

In wigs an allonge is a wig with locks of hair reaching to the shoulders
-- Wikipedia
Legal Definition
French law. When a bill of exchange, or other paper, is too small to receive the endorsements which are to be made on it, another piece of paper is added to it, and bears the name of allonge. Pard. n. 343; Story on P. N. 121, 151; Story on Bills, 204. See Rider.
-- Bouviers Law Dictionary
Legal Definition
When the endorsements on a bill or note have filled all the blank space, it is customary to annex a strip of paper, called an "allonge," to receive the further endorsements. Fountain v. Bookstaver, 141 III. 461, 31 N. E. 17; Haug v. Riley, 101 Ga. 372, 29 S. E. 44, 40 L It. A. 244 ; Bishop v. Chase, 156 Mo. 158, 56 S. W. 1080, 79 Am. St Rep. 515.
-- Black's Law Dictionary
Legal Definition
A paper attached to a negotiable instrument to provide space for further endorsements. See 141 HI. 461, 31 N. E. 17.
-- Ballentine's Law Dictionary