Deliberate obfuscation by the antis
The problem is that since 1944 when the German Army got Hitler's approval to use the MP44, Hitler renamed it the "Sturmgewehr" and the common English translation for that is "assault rifle" It could also be validly translated as "Storm Rifle". Soldiers "assault" or "storm" an objective, and so the rifle is aptly named. The US Army and the firearms community adopted the term to describe all rifles of the type, and it has been in use for over half a century.
The proper definition includes the words "selective fire", along with the other features common to this type of weapon.
When the anti gunners began demonizing military look alike rifles following the Stockton Ca. schoolyard shooting, many knowledgeable individuals point out to them that the rifle used was not an assault rifle, and wasted a lot of their breath explaining the difference. They didn't care. In order not to be accused of "lying", they started using the cumbersome term "semiautomatic assault rifle", knowing full well that this term would soon be dropped by newscasters who were more interested in a good sound byte than in being accurate. Semiautomatic assault rifle became "assault weapon" when they included certain handguns (those resembling SMGs), and this was the language that was adopted (verbatim) by legislators in Fed and state service when they proposed (and passed) legislation back in 94.
Assault Weapon is a totally made up term, one never used in the firearms community. Online dictionaries and later even print ones included the terms, with inaccurate definitions. Protest to the editors recieved the same response, that the dictionaries reflect the definition of the word, in popular usage.
The antis scored a major coup, by deliberatly using a misleading term, rather than the intellectually honest one in use by the military and firearms communities. Even today, a great many shooters use the terms assault rifle and assault weapon incorrectly, referring to semi auto rifles.
It is in our best interests, as public representatives of the firearms community (and don't think for a moment that this board isn't public) to ensure we use only the correct proper terms, and not the language of the enemies of freedom.