The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster] Poco a poco [It.] (Mus.) Little by little; as, poco a poco crescendo, gradually increasing in loudness. [1913 Webster]