keynote

keynote (http://definr.com/keynote)

     n 1: the principal theme in a speech or literary work
     2: a fundamental or central idea
     3: (music) the first note of a diatonic scale [syn: tonic]
     v 1: set the keynote of; "Comfort keynotes this designer's Fall
          collection"
     2: give the keynote address to (an audience)