One of the problems with English.....
Is everyone seems to make up definitions to fit the moment, or the agenda.
And, dictionaries give definitions "in popular use", whith no thought, or explanation that the "popular use" definition may be incorrect in the technical sense.
The definition I use, and the one I have been using since the 1960s is that an "assault rifle" is a rifle in the same general class as the German Sturmgewehre. The key defining elements are select fire (safe, semi & full auto), and the use of an "intermediate" power cartridge.
An intermediate power cartridge is one more powerful than a standard WWII pistol round, but not as powerful as a standard WWII infantry rifle/machine gun round. 7.62x39, 7.92x33 (the original) and even 5.56mm fit into this niche.
Up until the anti gun frenzy of the late 80 and early 90s, "assault rifle" was also stretched informally to include both the .22LR and sometimes centerfire semi auto copies of the original military assault rifles.
After the frenzy started, and the media began using the term "assault rifle", lots of folks tried to point out to them that they were technically wrong, and the rifles they were talking about were semi auto only, and therefore NOT actual assault rifles.
The media did, for a short time, use the term "semiautomatic assault rifle", but that proved to be too cumbersome a sound bite, so they came up with the term "assault weapon". Very close in sound to assault rifle, but subtlely different.
The term "assault weapon" applied to SEMI AUTO guns, that looked like the select fire military ones. In 1994, "assault weapon" became codified in Federal (and several states) law, and defined it as semi auto weapons with certain combinations of design features, such as (but not limited to) detachable magazine, pistol grip, bayonet lug, flash hider/suppressor, etc...
another factor complicating the correct use of the term assault rifle is the multiple definitions of the word "assault" in common usage. Some people think that any weapon used to assault (as in attack/shoot) someone is an assault weapon, and ought to be referred to that way. Technically correct in English usage, but totally wrong in contextual definifion.
"Assault" in assault rifle refers to a military assault on an objective. It is a direct translation of "Sturm" from Sturmgewehre. Sturm is translated as "assault" or "storm" (as in storming an objective, in the military sense).
Sturm is also translated as storm in the meterologial sense, so the correct translation depends on context. Something a great number of people (especially those in broadcast journalism) seem incapable of understanding.
The bottom line is an assault rifle is select fire, and shoots an intermediate power round. It can have a lot of other features, or not, but if doesn't have those main two, it's NOT an assault rifle, it is something else.