'unsustainably-managed' originates from Modern English, specifically the adverb 'unsustainably' (from 'unsustainable' + suffix '-ly') and the past-participle adjective 'managed' (from the verb 'manage'). 'unsustainable' ultimately traces to Latin via Old French where the root 'sustinere'/'sustain' meant 'to hold up', and the prefix 'un-' meant 'not'. 'manage' comes via Old French/Italian from Latin 'manus' meaning 'hand'.

'unsustainably-managed' was formed in Modern English by combining 'unsustainably' (itself from 'unsustainable' derived from Latin 'sustinere' through Old French) with 'managed' (from Old French/Italian 'manegiare'/'maneggiare'). The hyphenated compound evolved as writers linked an adverb and a past participle into a single adjectival modifier to describe operations or systems.

Initially, the components separately meant 'not able to be sustained' ('unsustainable') and 'to handle or control' ('manage'). Over time the compounded phrase came to mean specifically 'handled or run in a way that cannot be maintained over time', emphasizing the sustainability aspect of management.