Roaring Meg

noun3

1. •
   (historical) A large cannon; specifically, the large 15th cannon at Edinburgh Castle (more usually called ‘Mons Meg’), or the cannon used to defend Londonderry during the siege of 1688-9.
2. •
   (figurative, no longer used) Any large or impressive thing.

   • Musica est mentis medicina maestae, a roaring-meg against melancholy, to rear and revive the languishing soul […] — 1624
3. •
   (no longer used) A kind of spinning top.