/ ˌɪnstrəˈmentl; NAmE / adjective , noun
■ adjective
1.
instrumental (in sth / in doing sth) important in making sth happen :
He was instrumental in bringing about an end to the conflict.
2.
made by or for musical instruments :
instrumental music
► in·stru·men·tal·ly adverb
■ noun
1.
a piece of music (usually popular music) in which only musical instruments are used with no singing
2.
( grammar ) ( in some languages ) the form of a noun, pronoun or adjective when it refers to a thing that is used to do sth
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WORD ORIGIN
late Middle English : via French from medieval Latin instrumentalis , from Latin instrumentum , from the verb instruere , from in- upon, towards + struere pile up.