muffler and silencer

There really isn't one. The British call an automotive muffler, a silencer.

In the US, a silencer is more associated with fitting on the end of a gun to muffle the sound of the shot.

http://en.wikipedia.org/wiki/Muffler

And from my time with some British friends in Iraq, a muffler also fits on the end of a gun.

...and another 2 cents' worth --

Tuned exhaust systems are generally referred to as having "silencers" as opposed to "mufflers;" the distinction being, in tribal knowledge, flow properties and economy of design: Silencers are created with a bias towards greater flow and less weight; mufflers, less noise.

Indeed, in the glory days of 2-stroke motorcycle racing, a silencer consisted of nothing more than a perforated steel inner passage within a rockwool-packed alloy housing as part of the distalmost tuned length for the exhaust system. This, in theory, reduced noise output with little cost from the standpoint of weight and performance.

Helpful, perhaps?

Have a great day...

Yep. It's the Atlantic Ocean.