WordWeight : Weighing the Words

Pronunciation : In`stru*men"tal
Part of Speech : a.
Etymology : [Cf. F. instrumental.]
Definition : 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.)

Defn: 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." Macaulay. Sweet voices mix'd with instrumental sounds. Dryden.

3. (Gram.)

Defn: Applied to a case expressing means or agency; as, the instrumental case. This is found in Sanskrit 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 want of mathematical accuracy in an instrument.
Source : Webster's Unabridged Dictionary, 1913