paralexical

(not comparable)Pertaining to, or communicated through, paralexicon (parallel vocabulary, e.g. ritual or secret cant, formal jargon)

(not comparable)Pertaining to elements of speech beside the lexicon and grammar. Prosodic, paralinguistic.

Aural communication includes spoken words and paralexical sounds (groans, screams, whimpers); sound effects (wind, a car starting up and driving away); and music.

But the conventional nature of rhyme and metre, their essential arbitrariness, points to the fact that they themselves are also signifiers, albeit paralexical and to some extent parasyntactic.