Allonge

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.[1]

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

https://en.wikipedia.org/wiki/Allonge

one more meaning of "allonge" could be added from the way it's used in this text:

In the case of this airplane the "extension" is in the functionality of the airplane:

designed for tactical use, but its use can be extended to strategic use