Associativity

pertaining to or resulting from association.
tending to associate or unite.
Mathematics, Logic.

(of an operation on a set of elements) giving an equivalent expression when elements are grouped without change of order, as (a + b) + c = a + (b + c).
having reference to this property:
associative law of multiplication.

Historical Examples

It is subjected to certain conditions and, for example, to the rules of commutativity and associativity of addition.
The Foundations of Science: Science and Hypothesis, The Value of Science, Science and Method Henri Poincar

adjective
of, relating to, or causing association or union
(maths, logic)

being independent of the grouping of numbers, symbols, or terms within a given set, as in conjunction or in an expression such as (2 × 3) × 4 = 2 × (3 × 4)
referring to this property: the associative laws of arithmetic

adj.

1812, from associate (v.) + -ive.
associative
(ə-sō’shə-tĭv)
Of or relating to the property of an operation, such as addition or multiplication, which states that the grouping of numbers undergoing the operation does not change the result. For example, 3 + (4 + 5) is equal to (3 + 4) + 5. See also commutative, distributive.

programming
The property of an operator that says whether a sequence of three or more expressions combined by the operator will be evaluated from left to right (left associative) or right to left (right associative). For example, in Perl, the lazy and operator && is left associative so in the expression:
$i >= 0 && $x[$i] >= 0 && $y[$x[$i]] == 0
the left-most && is evaluated first, whereas = is right associative, so in
$a = $b = 42
the right-most assignment is performed first.
(2007-06-16)