Webster's Revised Unabridged Dictionary · 1913

Instrumental

Instrumental , adjective

[Compare French instrumental.]

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. — Shakespeare
2.
(Music) 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.
(Grammar) 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.
Collocations (1)
Instrumental errors , those errors in instrumental measurements, etc., which arise, exclusively from lack of mathematical accuracy in an instrument.