The word 'unavailability' is a modern English formation built upon the older adjective 'available'. Its core, 'avail', originates from the Latin verb 'valere', meaning "to be strong or worthy." This concept of worthiness evolved into the sense of being useful or at one's service. The prefix 'un-', a common Germanic negation, was added to reverse the meaning, creating 'unavailable' to describe something not accessible or obtainable. Finally, the Latinate suffix '-ability' was appended to nominalize the adjective, forming a word that precisely denotes the state or condition of not being accessible or at hand.

Structure: un (not) + avail (use, benefit) + ability (state of being) - un: A prefix of Germanic origin (Old English) meaning "not," used to form negatives. - avail: A verb from Old French 'a' (to) + 'valoir' (be worth), ultimately from Latin 'valere' (be strong, be worth). - ability: A noun-forming suffix from Latin '-abilitas', via Old French '-abilite', indicating a state or quality of being able.