The Collaborative International Dictionary of English v.0.48:
Britannic \Bri*tan"nic\, a. [L. Britannicus, fr. Britannia Great Britain.] Of or pertaining to Great Britain; British; as, her Britannic Majesty. [1913 Webster] BriteWordNet (r) 3.0 (2006):
Britannic adj 1: of Britain; "Her Britannic Majesty"