The word 'undeniable' is a layered construction built upon the core verb 'deny.' This verb entered English from Old French denier, tracing back to Latin denegare, a compound of de- ("completely") and negare ("to say no, refuse"). The suffix -able, also of Latin origin via French, was attached to create the adjective 'deniable,' meaning "capable of being denied." Finally, the Old English negative prefix un- was added to negate this capability, forming 'undeniable.' The logic of the word's evolution is a clear grammatical stacking: from the act of refusal (deny), to the potential for that act (deniable), to the negation of that potential (undeniable), ultimately arriving at its modern meaning of an irrefutable truth.

Structure: un (not) + deny (refuse to admit) + able (capable of) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - deny: A verb of Latin origin (via Old French denier), from Latin denegare ("to refuse, deny"). It functions as the core lexical root. - able: A suffix of Latin origin (via Old French -able), from Latin -abilis ("capable of, worthy of"). It functions as an adjective-forming suffix meaning "capable of being [verb]ed."