in·stru·men·tal 
(ĭn′strə-mĕntl)
(ĭn′strə-mĕntl)adj.
1. Serving as a means or agency; implemental: was instrumental in solving the crime.
2. Of, relating to, or accomplished with an instrument or tool.
3. Music Performed on or written for an instrument.
4. Grammar Of, relating to, or being the case used typically to express means, agency, or accompaniment.
5. Of or relating to instrumentalism.
n.
1.
a. Grammar The instrumental case.
b. A word or form in the instrumental case.
2. Music A composition for one or more instruments, usually without vocal accompaniment.
in′stru·mental·ly adv.