(French). A standpoint; a fulcrum; a position from which you can operate; a pretext to conceal the real intention. Literally the point of support.
“The material which gives name to the dish is but the point d'appui for the literary cayenne and curry-powder by which it is recommended to the palate of the 'cader.” —The Athenoeum.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894