The Collaborative International Dictionary of English v.0.48:
Undock \Un*dock"\, v. t. [1st pref. un- + dock.] (Naut.) To take out of dock; as, to undock a ship. [1913 Webster]WordNet (r) 3.0 (2006):
undock v 1: move out of a dock; "We docked at noon" [ant: dock] 2: take (a ship) out of a dock; "undock the ship" [ant: dock]