One obstacle President Barack Obama may face in proposing a new federal ban on assault weapons could lie in the use of the term “assault weapon” itself.

The label, applied to a group of firearms sold on the civilian market, has become so politicized in recent decades that where people stand on the gun issue can often be deduced by whether or not they use the term.

On Internet forums there is perhaps no more fiercely discussed topic than the question of what constitutes an assault weapon. And some argue that it would be impossible to come up with a definition comprehensive enough to effectively remove the weapons from the market.

Advocates of an assault weapons ban argue that the designation should apply to firearms like those used in the Newtown, Conn., shootings and other recent mass killings – semi-automatic rifles with detachable magazines and “military” features like pistol grips, flash suppressors, and collapsible or folding stocks.

Such firearms, they contend, were designed for the battlefield, where the goal is to rapidly kill as many enemy soldiers as possible, and they have no place in civilian life.

“When the military switched over to this assault weapon, the whole context changed,” said Tom Diaz, formerly of the Violence Policy Center, whose book about the militarization of civilian firearms, “The Last Gun,” is scheduled for publication in the spring. “The conversation became, ‘Is this the kind of gun you want in the civilian world?’ And we who advocate for regulation say, ‘No, you do not.’ ”

But Second Amendment groups – and many firearm owners – heatedly object to the use of “assault weapon” to describe guns that they say are routinely used in target shooting and hunting. The term, they argue, should be used only for firearms capable of full automatic fire, like those employed by law enforcement and the military – they prefer the term “tactical rifle” or “modern sporting rifle” for the semi-automatic civilian versions. And they argue that any attempt to ban “assault weapons” is misguided, since the weapons under discussion differ from many other firearms only in their styling.

“The reality is there’s very little difference between any sporting firearm and a so-called assault weapon,” said Steven C. Howard, a lawyer and firearms expert in Lansing, Mich.

The semantics of the assault weapon debate are so fraught that they can trip up even those who oppose a ban.

Phillip Peterson, a gun dealer in Indiana and the author of “Gun Digest Buyer’s Guide to Assault Weapons” (2008) said he had fought with his publishers over the use of the term in the title, knowing that it would only draw the ire of the gun industry.

After the passage of the 1994 federal ban on assault weapons, Peterson said, the gun industry “moved to shame or ridicule” anyone who used “assault weapon” to describe anything other than firearms capable of full automatic fire.

Equally controversial are the definitions for which firearms should qualify as assault weapons. Most assault weapons bans have been primarily aimed at rifles like the AR-15, a semi-automatic version of the military’s M-16 sold on the civilian market, although certain pistols and shotguns have also been included.

The most basic criteria have to do with a firearm’s ability to fire multiple rounds quickly. Because of this, the firearms included under any assault weapons ban are usually semi-automatic, meaning that a new round is automatically reloaded into the chamber but is not fired until the trigger is pulled again. The weapons also have detachable magazines, allowing them to fire 10, 20, 30 rounds or more without the need to insert a new magazine.

After that, however, the definition becomes more difficult. In calling for a renewed ban, Obama on Wednesday singled out “military-style” weapons.

That could include such features as a pistol grip, designed to allow a weapon to be fired from the hip; a collapsible or folding stock, which allows the weapon to be shortened and perhaps concealed; a flash suppressor, which keeps the shooter from being blinded by muzzle flashes; a muzzle brake, which helps decrease recoil; and a threaded barrel, which can accept a silencer or suppressor. Bayonet lugs or grenade launchers are also sometimes included.

But there is disagreement about which features are worrisome enough to include in a ban. And existing state bans differ in how many features they allow.