Appui \Ap`pui"\, n. (Man.) The mutual bearing or support of the hand of the rider and the mouth of the horse through the bit and bridle.

Point d'appui, any point of support or basis of operations, as a rallying point.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Appui \Ap`pui"\, n. [F., fr. L. ad + podium foothold, Gr. ?, dim. of ?, ?, foot.]

A support or supporter; a stay; a prop. [Obs.]

If a vine be to climb trees that are of any great height, there would be stays and appuies set to it. --Holland.

Point d'appui. [F., a point of support.]

(Mil.)
   (a) A given point or body, upon which troops are formed, or by which are marched in line or column.
   (b) An advantageous defensive support, as a castle, morass, wood, declivity, etc.

Source: Webster's Revised Unabridged Dictionary (1913)