Ethring was presumably founded at some point after the creation of the realm of Gondor in II 3320, as shown in the timeline above, but we have almost no hard evidence to work with. The settlement here may even predate Gondor (though if so, the Gondorians seem to have renamed it). All we can say for sure is that Ethring existed at the end of the Third Age.

Tolkien never directly translates the name Ethring, but at least it seems clear that the -ring element of its name (literally meaning 'cold') is connected to the river Ringló that ran through it.

The initial Eth- element is harder to translate; it is perhaps connected to ethir 'outflow of a river'. If so, in the case of Ethring it would presumably describe the place where the Ringló flowed out from the mountain valleys into the plains east of Lamedon. Alternatively the entire name may be a worn-down form of Ethraid Ringló, 'crossings of Ringló', an entirely suitable name given Ethring's location.