adj. & n.
adj. 1 (usu. foll. by to, in, or in + verbal noun) serving as an instrument or means (was instrumental in finding the money). 2 (of music) performed on instruments, without singing (cf. VOCAL). 3 of, or arising from, an instrument (instrumental error). 4 Gram. of or in the instrumental.
n. 1 a piece of music performed by instruments, not by the voice. 2 Gram. the case of nouns and pronouns (and words in grammatical agreement with them) indicating a means or instrument. instrumentalist n. instrumentality n. instrumentally adv.
[ ME f. F f. med.L instrumentalis (as INSTRUMENT) ]