The Collaborative International Dictionary of English v.0.48:

Capapie \Cap`*a*pie"\, adv. [OF. (?) cap-a-pie, from head to
   foot, now de pied en cap from foot to head; L. pes foot +
   caput head.]
   From head to foot; at all points. "He was armed cap-a-pie."
   --Prescott.
   [1913 Webster]