Originally Posted by Windage and Elevation
"Silencer" is the term that was used by the manufacturers (and users) for many decades after they first appeared and is the legal term used in the regulations. "Suppressor" came into use mainly because lots more civillians started buying and using them in the last few decades.
A lot of buyers were upset when their expensive new toy didn't work quite as effectively as James Bond's did on the big screen. Seems "silencer" tends to make people think the product eliminates all noise from the shot. The manufacturers and the magazine articles reviewing them started using the term "suppressor" as it more accurately describes what is happening to the sound. It also lets people understand that not all sound is eliminated, just reduced. Less unhappy customers.
Legally there is no difference. ANY device designed to reduce the noise of a shot is considered a silencer no matter what you call it or how ineffective it is.