Definition of: instrumental

(in′strə·men′təl) adjective
1. Serving as a means or instrument; serviceable.
2. Fitted for or produced by musical instruments.
3. Traceable to a mechanical instrument, as errors in observation or measurement.
4. Gram. Pertaining to a case of the noun, as in Sanskrit, indicating the means or instrument by or with which something is done.
—noun Gram.
1. The instrumental case.
2. A word in this case.