the word 'unaccountable' is a layered construction built upon the core concept of 'account'. this root, entering english via old french from latin 'computare' (to calculate), evolved to mean giving a reasoned explanation. the suffix '-able' attaches to form 'accountable', meaning "capable of being explained or held responsible". the old english negative prefix 'un-' is then added to negate this entire concept. thus, the literal morpheme sequence "not + explain + capable of" logically yields the modern meanings of being inexplicable or exempt from the normal requirement to justify actions. this etymological journey showcases how english combines germanic and romance elements to create precise abstract adjectives.

Structure: un (not) + account (explain) + able (capable of) - un: a prefix of germanic origin (old english) meaning "not". - account: from old french 'acunter', based on latin 'computare' meaning "to calculate, reckon". in this word, it carries the sense of "to explain or give a reason". - able: a suffix from latin '-abilis', via old french, meaning "capable of, fit for".