the word 'unsustainable' is a modern english formation built upon the established adjective 'sustainable'. its core, 'sustain', originates from the latin verb sustinēre, meaning "to hold up from below, to support," which itself is a compound of sub- (from below) and tenēre (to hold). the suffix '-able' was attached in late middle english via old french from latin -ābilis, creating the meaning "capable of being supported or maintained." finally, the old english prefix 'un-' is applied to negate the entire concept, resulting in the contemporary meaning that describes a state or practice which cannot be upheld or continued, especially without causing depletion or harm.

Structure: un (not) + sustain (support) + able (capable of) - un: a prefix of germanic origin, meaning "not," used to give a negative force. - sustain: from latin sustinēre (to hold up, support), acting as the core verb root. - able: a suffix from latin -ābilis, meaning "capable of, fit for," forming adjectives.