1A name given to any of various large pieces of ordnance. Any similarly large cannon.
During the English Civil War applied specifically to a mortar used by the Royalist forces.
2The cannon used to defend the town of Londonderry in Ireland during the siege of 1688–9.
According to tradition the gun was presented to the town by the Fishmongers' Company of London in 1642, but there is no contemporary evidence of the name being applied to this cannon in the 17th-cent.
3A noisy stream or flow of water. Chiefly as a proper name of streams.
Late 16th century (in an earlier sense). From roaring + Meg.