associative

Pertaining to, resulting from, or characterised by association; capable of associating; tending to associate or unite.

(of a binary operator *) Such that, for any operands a, b and c, (a * b) * c = a * (b * c); (of a ring, etc.) whose multiplication operation is associative.

Addressable by a key more complex than an integer index.

“AWK's associative arrays may be indexed by strings.”