'appliant' originates from Latin, specifically the word 'applicare,' where 'ad-' meant 'to/toward' and 'plicare' meant 'to fold' (sense developing to 'attach' or 'apply').

'appliant' developed via Old French/Middle French participial forms (e.g. French 'appliant' or verbs like 'applier') and entered English usage as a rare/technical or legal term, eventually stabilizing as the modern form 'appliant'.

Initially it was tied to the idea of 'attaching' or 'folding toward' (from Latin), then to 'apply' in the sense 'to put to use' or 'to petition', and in modern use it came to mean 'one who applies' or 'applying' (the latter being archaic compared to 'applicable').