Pronunciation: (in"stru-men'tl),[key] —adj. 1. serving or acting as an instrument or means; useful; helpful.
2. performed on or written for a musical instrument or instruments: instrumental music. 3. of or pertaining to an instrument or tool.
4. Gram. a. (in certain inflected languages, as Old English and Russian) noting or pertaining to a case having as its distinctive function the indication of means or agency, as Old English beseah blīthe andweitan “looked with a happy countenance.”
b. noting the affix or other element characteristic of this case, or a word containing such an element.
c. similar to such a case form in function or meaning, as the Latin instrumental ablative, gladiō, “by means of a sword.”
d. (in case grammar) pertaining to the semantic role of a noun phrase that indicates the inanimate, nonvolitional, immediate cause of the action expressed by a verb, as the rock in The rock broke the window or in I broke the window with the rock.
—n. 1. Gram. a. the instrumental case.
b. a word in the instrumental case.
c. a construction of similar meaning.
2. a musical composition played by an instrument or a group of instruments. Cf. vocal (def. 8).