in·stru·men·tal·i·ty /ˌin-strə-mən-'ta-lə-tē, -ˌmen-/ n pl -ties
1: something through which an end is achieved or occurs
damages incurred in a single incident through an instrumentality owned by the employer
2: something that serves as an intermediary or agent through which one or more functions of a larger controlling entity are carried out: a part or branch esp. of a governing body compare alter ego
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.