acting as an instrument; serving as a means; contributing to promote; conductive; helpful; serviceable; as, he was instrumental in conducting the business.-pertaining to, made by, or prepared for, an instrument, esp. a musical instrument; as, instrumental music, distinguished from vocal music.-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.