reciprocate

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"
    

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]
    

Reciprocate \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. --Cowper.
   [1913 Webster]
    

127 Moby Thesaurus words for "reciprocate":
      accord, act in concert, act together, affiliate, agree, agree with,
      ally, alternate, amalgamate, answer, answer to, associate,
      back and fill, band, band together, bandy,
      battledore and shuttlecock, be in league, be quits with, change,
      chime in with, club together, coact, coalesce, coequal,
      collaborate, collude, combine, come and go, come back at, commute,
      compensate, complement, concert, concord, concur, confederate,
      consolidate, conspire, cooperate, correspond, correspond to,
      cotton to, counter, counterchange, do business with, ebb and flow,
      empathize, equal, exchange, fall in with, federate, fuse,
      get along, get along with, get back at, get even with,
      get heads together, get on with, get together, give and take,
      give in exchange, give in return, go partners, hang together,
      harmonize, harmonize with, hit back at, hitch and hike,
      hold together, hook up, identify with, interchange, join, join in,
      join together, keep together, league, league together, logroll,
      make common cause, match, merge, partner, pass and repass,
      pay back, permute, play ball, pull together, put heads together,
      recompense, repay, requite, respond, respond to, retaliate, retort,
      return, return the compliment, ride and tie, seesaw, shuttle,
      shuttlecock, sing in chorus, stand together, strike back, swap,
      swing, switch, sympathize, team up, teeter, teeter-totter,
      throw in together, tie in, tie up, to-and-fro, trade, transpose,
      understand one another, unite, unite efforts, wax and wane,
      wibble-wabble, wigwag, work together, zigzag