DICT.TW Dictionary Taiwan

 reciprocating motion
 往復運動

 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.