A flash suppressor, also known as a flash guard, flash eliminator, flash hider, or flash cone,
While Wiki (or anybody else) is free to print their own definition, and the terms are all too often used interchangeably in conversation, and the maker or something can call it what ever they want, to those of us who worked with the items in the military (during the 1970) we followed the terminology used during WW II and later. And for us, there was a clear difference between a flash hider and a flash suppressor.
Both have the same purpose, but there is a slight mechanical difference in their construction. The solid cone shaped device attached to the end of the barrel of the M2HB .50 cal machine gun, and the M3A1 .45acp SMG ("Grease gun" and to one variant of the M1 Garand, as well as the device on the British "Jungle Carbine" were all called "Flash hiders". Every time.
The device on the M14 and M16 are different, they have "holes" (slots" in the body, and are called "flash suppressors".
You can look in the Army manuals, and in other places and see them always referred to by different names, because they are different items.
That being said, people today tend to use the terms interchangeably, with no real world effect, other than giving me the impression that they don't really know what they are talking about...
Ask someone what motor they have in their car. Most will say without hesitation a 4.6. 8 cylinder and give the size in CuIN or in liters or CC, and think nothing of it. But technically its not a motor, it's an engine. And going further, its an internal combustion engine of (details of displacement) size.
Ask a car geek what motor is in his car, and he might ask back, "Which one?? The starter motor? windshield wiper motor?? power window motor??
We do it with clips and magazines, too. and I'm done wasting arguments over it. It happens, I point out the correct terms, once, then move on (or pretend to move on...
it constantly irritates me when I read the term "bullet clips" in the text of a law..
)
A flash hider and a flash suppressor are there to reduce the effect of the flash on the shooter's vision, and the people near him, on his side. The hider is true to its name, it used solid metal to "hide" part of the flash from the shooter's vision.
Flash supppressors don't "hide", they change the appearance of the flash to the shooter (and those in line with or behind them), from a "ball" to a "cross" type shape the arms of which are the flash that escapes through the slots or holes. For military use this is efficient enough, and also allows for a more durable construction. A flash hider's cone must be relatively thin metal due to weight considerations, and is more easily bent or damaged than the usual flash suppressor's heavier construction. A flash suppressor can be more heavily built, because it can be smaller than a flash hider and still do its job effectively.
I think the most likely reason the M1 Garand (and earlier rifles we used) didn't have flash hiders or suppressors is that they weren't considered a needed thing for general duty use. Rate of fire matter, too.
Prior to our modern era, you find flash hiding devices on more machine guns than on rifles. Bolt actions, and even the semi auto Garand cannot be fired fast enough, long enough to create a sustained fireball (affecting the night vision of everyone seeing it) the way a full auto does.
The M14 and the M16 are capable of full auto fire, so reducing the visible flash of bursts matters more than reducing the flash of individual shots fired from a Springfield or even a Garand.
PLUS, experience is a teacher, though some lessons are learned slower than others, after WWII, we had a LOT of people with personal experience in low light combat situations, some of them even got into decision making slots in the Ordnance organizations.
And, going back to the Garand, a medium burn rate powder .30-06, fired from a 24" barrel. semi auto, as fast as you can, 8 shots, isn't the same degree of flash as a 3second (or longer) burst from a belt fed.
Think about what you see in the dark when the other guy in your hole shoots, or if you're where that machinegun's flash is in the corner of your eye..reducing that, for the guy who isn't shooting has military value, too.
And today, with our M4 class guns, burning 30some grains of powder out of 14" or even 10" barrels. Something to cut the flash is even more important.