The Collaborative International Dictionary of English v.0.48:

Capias \Ca"pi*as\, n. [L. thou mayst take.] (Low)
   A writ or process commanding the officer to take the body of
   the person named in it, that is, to arrest him; -- also
   called writ of capias.
   [1913 Webster]

   Note: One principal kind of capias is a writ by which actions
         at law are frequently commenced; another is a writ of
         execution issued after judgment to satisfy damages
         recovered; a capias in criminal law is the process to
         take a person charged on an indictment, when he is not
         in custody. --Burrill. Wharton.
         [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CAPIAS, practice. This word, the signification of which is "that you take,"
is applicable to many heads of practice. Several writs and processes,
commanding the sheriff to take the person of the defendant, are known by the
name of capias. For example: there are writs of capias ad respondendum,
writs of capias ad computandum, writs of capias ad satisfaciendum, &c., each
especially adapted to the purposes indicated by the words used for its
designation. See 3 Bl. Com. 281; 3 Bouv. Inst. n. 2794.