reciprocate

英 [rɪ'sɪprəkeɪt] 美[rɪ'sɪprəket]

• vt. 报答；互换；互给
• vi. 往复运动；互换；酬答；互给

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"