Source : Webster's Revised Unabridged Dictionary (1913)

Poco \Po"co\, adv. [It.] (Mus.)
   A little; -- used chiefly in phrases indicating the time or
   movement; as, poco pi[`u] allegro, a little faster; poco
   largo, rather slow.

   {Poco a poco} [It.] (Mus.) Little by little; as, poco a poco
      crescendo, gradually increasing in loudness.