reciprocating motion

Reciprocate \Re*cip"ro*cate\ (r[-e]*s[i^]p"r[-o]*k[=a]t), v. i.
   [imp. & p. p. {Reciprocated}
   (r[-e]*s[i^]p"r[-o]*k[=a]`t[e^]d); p. pr. & vb. n.
   {Reciprocating}.] [L. reciprocatus, p. p. of reciprocare. See
   {Reciprocal}.]
   To move forward and backward alternately; to recur in
   vicissitude; to act interchangeably; to alternate.
   [1913 Webster]

         One brawny smith the puffing bellows plies,
         And draws and blows reciprocating air.   --Dryden.
   [1913 Webster]

   {Reciprocating engine}, a steam, air, or gas engine, etc., in
      which the piston moves back and forth; -- in distinction
      from a rotary engine, in which the piston travels
      continuously in one direction in a circular path.

   {Reciprocating motion} (Mech.), motion alternately backward
      and forward, or up and down, as of a piston rod.
      [1913 Webster]