Seeming to go on for ever. The key word is seeming. Almost nothing really has no end, so when we call something unending we are saying how it feels to the person living through it — usually badly. It goes with suffering, noise, waiting, complaining, rain, war, paperwork: 'unending pain', 'her unending questions', 'the unending stream of bad news'. Because the feeling is so often one of being worn down, the word carries a tired, heavy tone even when the thing itself is neutral. That said, it does turn up in warm or grand language too — 'unending love', 'unending gratitude', 'the unending beauty of the sky' — where the tone lifts and it means something like 'that will never run out'. You will meet that use in songs, poems, wedding speeches and religious writing more than in ordinary talk. Compare its neighbours: endless is the everyday word and sounds most natural in speech; never-ending is the friendly spoken one ('a never-ending story'); eternal and everlasting are grander and more often about time itself. Unending is a little more literary than endless and is more often written than said.