How many letters does the top answer for “a reciprocal relation between two or more things” have?

The most common answer is correlation (11 letters).

Crossword clue: a reciprocal relation between two or more things

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

correlation 11 letters wn-def

a reciprocal relation between two or more things

correlativity 13 letters wn-def

a reciprocal relation between two or more things