| Definition -
A case that is used to show that a noun is the instrument or the means by which the subject accomplishes an action.
This case answers the question "by what means?" Thus, for example, in Russian when someone uses an instrument to accomplish something, this case is used.
1. English doesn't have this case. Instead it uses adverbial phrases that begin with with, by, or using followed by a noun denoting the instrument, e.g. I hit the jackass with a hammer.