In the US ATF sends you to jail for an unregistered silencer.
As you can see Advanced Armament calls their products silencers.
http://www.advanced-armament.com/
From Gemtech's website.
Welcome to the home page of Gemtech. As one of the oldest and most trusted world leaders in modern firearm silencer design, we maintain a staff of experienced designers and production engineers to bring you the latest in silencer technology for government, law enforcement, military and qualified civilian applications. Gemtech is a veteran-owned business.
Everyone in the industry has used the term silencer since Hiram Maxim himself. It is the correct term.
http://guns.connect.fi/gow/silencer.html
Sound supressor, sound moderator, muffler etc. would also be a correct term.
Well known authors have written books on the item.
http://www.amazon.com/Silencer-Perfo.../dp/0873649095
The US Military calls them silencers.