[adj] of or relating to or responsible for administration
ADMINISTRATIVE is a 14 letter word that starts with A.
Webster's 1913 Dictionary
Definition:
\Ad*min"is*tra`tive\, a. [L. administrativus: cf.
F. administratif.]
Pertaining to administration; administering; executive; as,
an administrative body, ability, or energy. --
{Ad*min"is*tra`tive*ly}, adv.
WordNet Dictionary