'Commitative' is a case!

Commitative: Commitative indicates who or what an action is done with, in the sense of "together with" (for example, I went to the store with my sister) ...
members.tripod.com/~Nik_Taylor/Conlang/Case.html

Sumer-phonology
**daa =commitative** "with" ši=terminative "to or until" ta= ablaitive "from" ... -da= Commitative "with" -šč, ši; Terminative "up to, toward" ...
users.cwnet.com/millenia/Sumer-Grammar.htm

Commitative,Instr,Manner. Language. Basque; chivenda; Finnish; Turkish; Welsh. Back to languages table of contents. Back to topics table of contents ...
www.uiowa.edu/~linguist/classes/typology99/languages/topics...

Commitative noun phrases in subject position have the form NP-c NP-m, ... However commitative noun phrases are generally accompanied by numerical ...
celia.cnrs.fr/FichExt/Am/A_04_06.pdf

s + m > rm (for example, **when adding the commitative case ending** to an s-stem) Notes: commitative expresses both "and" as well as "with", "together with" ...
steen.free.fr/relay8/silindion.html