re·cip·ro·cate /rɪˈsɪprəˌket/
 (vt.)互換,交換,報答,使往復運動(vi.)往復運動,互換,酬答


 Re·cip·ro·cate v. i. [imp. & p. p. Reciprocated p. pr. & vb. n. Reciprocating.]  To move forward and backward alternately; to recur in vicissitude; to act interchangeably; to alternate.
 One brawny smith the puffing bellows plies,
 And draws and blows reciprocating air.   --Dryden.
 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.


 Re·cip·ro·cate, v. t. To give and return mutually; to make return for; to give in return; to interchange; to alternate; as, to reciprocate favors.

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 reciprocate
      v 1: act, feel, or give mutually or in return; "We always invite
           the neighbors and they never reciprocate!"
      2: alternate the direction of motion of; "the engine
         reciprocates the propeller"