The Griffon engine is the same as the Merlin engine, however it has a supercharger fitted to help it breathe at higher altitudes. The Spitfire has one of them, the Shackleton has four, as does the Lancaster. The Shackleton was a submarine detection system which used to patrol the perimeter of the UK looking for enemy submarines.
There was one at Coventry Airbase which I volunteered on a few times, most notably fitting the refurbished tail gear. It would occasionally run its four Griffons up on show days:
One thing I'll say is that if I never have to touch another piece of Whitworth thread ever again, I'll be happy.
The Merlin and Griffon engines are completely different. The Merlin is a 27ltr V12 and first ran in the early 30s, whilst the Griffon is 37ltrs and didn't run until 1939. Both were supercharged and both fitted to the Spitfire at different stages of its development. The Shackleton only ever used the Griffon.