from pirate + -ous + -ly
From: Select Pleas in the Court of Admiralty.
Volume I, The Court of the Admiralty of the West, (1390-1404)
And The High Court of Admiralty (1527-1545)
Edited by Reginald G. Marsden, 1894.
Part II, Extracts from the Records of the High Court of Admiralty, Re Shenu