the word 'unusable' is a modern english formation built upon the well-established adjective 'usable.' its logic is transparently compositional, layering negation onto capability. the core root 'us-' originates from latin 'uti,' meaning to employ or make use of, which passed into english via old french. the suffix '-able,' also of latin origin, attaches to verbs to denote fitness or potential. finally, the old english prefix 'un-' is prefixed to negate the entire concept, creating a word that literally means "not capable of being used." this tripartite structure exemplifies how english freely combines elements from its germanic and romance lineages to create precise descriptive terms.

Structure: un (not) + us (use) + able (capable of) - un: a prefix of germanic origin (old english) meaning "not," serving a negating function. - us: a root derived from the latin verb 'uti' (to use), representing the core concept of employing something. - able: a suffix of latin origin (via old french) from '-abilis,' meaning "capable of, fit for," forming adjectives.