instrumental

adj

1. Essential or central; of great importance or relevance.

   “He was instrumental in conducting the business.”

   “The head is not more native to the heart, The hand more instrumental to the mouth”

   “Few songwriters have been as instrumental in creating the mold for American music.”

   “[...] Prosser was instrumental in the decision in 2010 to recommence publication of an annual health and safety report, following a period when it had fallen into abeyance.”

2. Serving as an instrument, medium, means, or agency.

   “Maxwell started back to his study, feeling that kind of satisfaction which a man feels when he has been even partly instrumental in finding an unemployed person a remunerative position.”

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

   “instrumental music”

   “an instrumental part”

   “Sweet voices mix'd with instrumental sounds.”

   “He defended the use of instrumental music in public worship.”

4. Applied to a case expressing means or agency, generally corresponding to the English use of prepositions such as by, with, through, or by means of with the objective case.

   “the instrumental case”

noun

1. The instrumental case.
2. A composition written or performed without lyrics or singing, using a lead instrument to replace vocals.

   “I recommend this album in the face of the fact that five of the eleven songs are the purest filler, dull instrumentals with a harmonica rifling over an indifferent rhythm section. The rest is magnificent […]”

3. A pause in the vocals of a song, usually occurring midway through, in which a musical instrument replaces the vocals.