adjective

1. serving as a means; helpful (in bringing something about)
2. of or performed with an instrument or tool
3. of, performed on, or written for a musical instrument or instruments
4. of or in keeping with instrumentalism
5. Gram. designating, of, or in the case of nouns, pronouns, or adjectives expressing means or agency

Etymology: ME < MFr < ML instrumentalis

noun

1. a composition for a musical instrument or instruments
2. Gram.
   1. the instrumental case: this case is expressed by inflection in Old English, Sanskrit, Russian, etc., and in English with the prepositions by or with (Ex.: OE ðȳ spere, “by the spear, with the spear”)
   2. a word or phrase in this case