noun
: a law indicating immateriality in the grouping of variables ; specifically : any law of the form (φ R χ) Rψ=φR (χ R ψ) where φ, χ, ψ are variables and R a dyadic operator [as (a +b)+c=a+(b+c) in arithmetic or ( p v q )v r.≡.p v( q v r ) in the propositional calculus] — called also principle of association