| 4. | Grammar. | 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. | |
[in-struh-men-tl] 
strəˈmɛn