Something that seems to last forever or goes on without stopping; endless.
From the prefix 'un-' (not) combined with 'ending' (the present participle of 'end'). This is a straightforward English compound that became common in the 1800s as a poetic way to mean 'endless' or 'eternal.'
While 'endless' and 'unending' mean similar things, 'unending' sounds more dramatic and poetic—which is why you'll often hear it in songs and poems rather than everyday speech like 'the unending rain' instead of 'the endless rain.'
Complete word intelligence in one call. Free tier — 50 lookups/day.