'unrelieved' is formed in English by adding the prefix 'un-' to the past participle 'relieved' (from the verb 'relieve').

'relieve' comes from Old French 'relever' / 'reliever' (to raise up, to relieve), ultimately from Latin 'relevare' (re- + levare, from 'levis' meaning 'light'), and the adjective 'unrelieved' developed in Modern English by prefixing 'un-' to the past participle form.

Originally rooted in the sense 'to raise up' or 'make lighter' (Latin), the verb 'relieve' came to mean 'to ease or reduce (pain, burden)'; 'unrelieved' thus came to mean 'not eased or diminished' (and by extension 'complete' or 'absolute').