the word 'unanswerable' is a layered construction built upon the old english core 'answer'. the old english 'andswaru' itself is a compound of 'and-' (against) and 'swerian' (to swear), conveying the sense of a sworn statement given in return. the suffix '-able', entering english via old french from latin '-abilis', attaches to verbs to denote capability. the negative prefix 'un-', of germanic origin, is then applied to negate this capability. thus, the literal morphemic sequence "not + reply + capable of" logically evolved into the modern abstract meaning describing a question or argument so definitive that no adequate reply is possible.

Structure: un (not) + answer (reply) + able (capable of) un- (old english, prefix expressing negation); answer (old english, from 'andswaru', meaning a reply or response); -able (latin via old french, suffix forming adjectives meaning 'capable of, fit for').