(grammar) The instrumental case.

A composition written or performed without lyrics, sometimes using a lead instrument to replace vocals.

Essential or central; of great importance or relevance.

“He was instrumental in conducting the business.”

Pertaining to, made by, or prepared for, an instrument, especially a musical instrument (rather than the human voice).

“An instrumental part”

(grammar) Applied to a case expressing means or agency, generally indicated in English by by or with with the objective.

“the instrumental case”