The Collaborative International Dictionary of English v.0.48:

high-up \high-up\ n.
   an important or influential person.

   Syn: very important person, VIP, dignitary, panjandrum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

high-up
    n 1: an important or influential (and often overbearing) person
         [syn: very important person, VIP, high-up,
         dignitary, panjandrum, high muckamuck]