the word 'unintelligibly' is built upon the core latin verb intelligere, meaning 'to understand, comprehend'. this verb itself is a compound of inter- (between, among) and legere (to gather, choose, read), suggesting the act of discerning meaning by selecting among elements. the suffix -ibilis was added to form the adjective 'intelligible', meaning 'able to be understood'. the negative prefix un-, of germanic origin but widely used in english, was then attached to create its opposite. finally, the adverbial suffix -ly (from old english -lice) was applied to the base 'unintelligible' to form the adverb describing the manner of being impossible to understand.

Structure: un (not) + intellig (understand) + ibly (in a manner of) un- (a prefix of negation, from old english and latin); intellig- (a root meaning 'understand', from latin intelligere); -ibly (an adverbial suffix meaning 'in a manner that can be', from latin -ibilis via old french).