exchange of contracts vs reciprocation

exchange of contracts

noun
  • The act of exchanging contracts. 

  • The point or stage at which a conveyancing contract comes into existence between negotiating parties for the carrying out of a disposition of an estate in land; usually requiring the payment of a deposit. 

reciprocation

noun
  • The act of reciprocating; interchange of acts; a mutual giving and returning 

  • Alternate recurrence or action; as, the reciprocation of the sea in the flow and ebb of tides; oscillation. 

How often have the words exchange of contracts and reciprocation occurred in a corpus of books? (source: Google Ngram Viewer )