Motuna, or Siwai, is a Papuan language of Bougainville Province, Papua New Guinea.
[1]: 115 Siwai is an agglutinating language that undergoes a substantial amount of morphophonological fusion.
It shows extremely complex prefixation and suffixation in verbs, kinship terms, classifiers, and numerals.
[1]: 115 Siwai exhibits five genders: masculine, feminine, diminutive, local, and manner.
Siwai has four types of valency structure:[1]: 118–9 Some verbs are ambitransitive and take either active or middle voice.