APPUI n.
t d'appui. Etym: [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.
AUXILIARY a. 2 definitions
Conferring aid or help; helping; aiding; assisting; subsidiary; as auxiliary troops. Auxiliary scales (Mus.), the scales of relative or attendant keys. See under Attendant, a. -- Auxiliary verbs (Gram.). See Auxiliary, n., 3.