This was briefly, in 2373, the home of an underground Maquis base, one of the last surviving pockets of the Maquis after the Dominion massacred the resistance group. The Maquis at the base supposedly fired a volley of cloaked missiles towards Cardassia Prime as a final act of revenge.
Captain Benjamin Sisko persuaded Michael Eddington to guide him to the planet and help him stop the missiles, whereupon he discovered that they did not in fact exist, and the message announcing the attack was to signal Eddington that the Maquis there were still alive.
Unfortunately, the Jem'Hadar had discovered and overran much of Athos IV as well, and Eddington was killed during the evacuation. The remaining Maquis at the base were taken to Federation space aboard Sisko's runabout. (DS9: "Blaze of Glory")
"AH-thoes" was the pronunciation for this planet's name from the script pronunciation guide. 
Athos IV was mentioned in the final draft script of TOS: "The Galileo Seven", where it was apparently not uninhabited as it was said to be the homeworld of "the Lake People", who were characterized as having large, distinctive axes.