In·stru·men·tal a.
 1. Acting as an instrument; serving as a means; contributing to promote; conductive; helpful; serviceable; as, he was instrumental in conducting the business.
 The head is not more native to the heart,
 The hand more instrumental to the mouth.   --Shak.
 2. Mus. Pertaining to, made by, or prepared for, an instrument, esp. a musical instrument; as, instrumental music, distinguished from vocal music. “He defended the use of instrumental music in public worship.”
    Sweet voices mix'd with instrumental sounds.   --Dryden.
 3. Gram. Applied to a case expressing means or agency; as, the instrumental case. This is found in Sanskrit and Russian as a separate case, but in Greek it was merged into the dative, and in Latin into the ablative. In Old English it was a separate case, but has disappeared, leaving only a few anomalous forms.
 Instrumental errors, those errors in instrumental measurements, etc., which arise, exclusively from lack of mathematical accuracy in an instrument.
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