reciprocate  verb FORMAL
 to share the same feelings as someone else, or to behave in the same
 way as someone else
 He loved and admired her and felt that his love was reciprocated. [T]
 If you show trust to somebody, that trust will be reciprocated. [T]
 We invited them to dinner and a week later they reciprocated. [I]

 (formal) If a part of a machine reciprocates, it moves backwards and
 forwards.
 Some electric razors have reciprocating heads.

 reciprocal  adjective FORMAL
 A reciprocal action or arrangement involves two people or groups of
 people who behave in the same way or agree to help each other and give
 each other advantages.
 The two superpowers agreed to a reciprocal reduction of nuclear
 weapons.
 Many states have passed laws that will allow nationwide reciprocal
 banking.

 reciprocally  adverb FORMAL

 reciprocation  noun [U] FORMAL
 She had loved him almost all her life without reciprocation (=he did
 not have the same feelings for her).

 reciprocity   noun [U] FORMAL
 Reciprocity is behaviour in which two people or groups of people give
 each other help and advantages.
 The two countries have signed a new agreement based on reciprocity
 in trade.