There are two Rio Treaties

1) Rio Treaty (Inter American Treaty Of Reciprocal Assistance) that was signed on September 2 1947. This originally was ratified by all 21 American Republics. The treaty said that if any threat of armed conflict or aggression was made against one of the signatory nations by a member or non member state, it would be seen as an attack against all. No member was to use force without consent of the others. Measures against aggressors would need a two thirds majority. It differed from previous Inter American treaties in that it is a regional treaty within a larger international organisation, it recognises the Security Council of the United Nations.

2) Rio Treaty (Convention on Biological Diversity). An international environmental agreement that was approved at the Earth Summit in Rio de Janerio 1992. The aim of this is conservation of the planets biodiversity by fair use of its resources.

You spell it like "Reciprocal".

The harsh feelings between the atheist and the Christian were a definite reprocity.

Are you looking for the word "TREATY?"