definition instrumental
WordReference Random House Unabridged Dictionary of American English Â© 2016. inâ¢struâ¢menâ¢tal (inâ²strÉ menâ²tl), adj. 1  serving or acting as an instrument or means; useful; helpful. 2  Music and Danceperformed on or written for a musical instrument or instruments:instrumental music.  of or pertaining to an instrument or tool.