In Igboland we have ìsú and ìdú: Ìsúikwuato, Ìsú Njaba, Ìsúochi, Ìsú Awa, Ìsú Onicha; while on the other hand we have Ìdú Osobile, Ìdú Obosi-Uku, Ìdú-umuje (Idumuje), Ìdú-umuobi (Idumu Obi), etc. This all indicating a unit or assembly of people. Ìsú Ikwuato: Forest unit of three lineages or Ìdú Obosi-Uku: Forest unit of the Great Obosi. Call it forest unit, forest gathering, or forest assembly all the same.
Some may ask how /s/ turned to /d/ and vice versa but remember that’s the dynamics of language. For instance, when it comes to the word follow, some places say ‘Dòó’ instead the commonly used ‘Sòó’. There are many examples that I’m sure others can give.