In the US ATF sends you to jail for an unregistered silencer.
As you can see Advanced Armament calls their products silencers.
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.
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.