the word 'unaccountably' is built upon the core verb 'account', which traces back to the latin 'computare', meaning to calculate or reckon. the prefix 'un-', of old english origin, applies a straightforward negation, transforming the meaning to "not able to be reckoned or explained." the adverbial suffix '-ably', derived from the latin '-abilis' through old french, then modifies this state into a descriptor of manner. thus, the literal construction "not + explainable + in a manner" evolved into its modern abstract sense of describing something that occurs in a puzzling or inexplicable way.

Structure: un (not) + account (explain) + ably (in a manner of) - un: a prefix of germanic origin (old english) meaning "not," serving a negating function. - account: from old french 'aconter', based on latin 'computare' (to calculate, reckon), functioning as the core verb root meaning "to explain or consider." - ably: an adverbial suffix of latin origin (via old french '-able' + '-ly'), indicating the manner or capability of an action.