the compound "thoroughgoing" is a native english formation. its first element, "thorough," evolved from the old english adverb/preposition thurh, meaning "through," which developed an adjectival sense of "complete" or "penetrating every part." the second element, "going," is the present participle of the verb "go," used here to form an adjective describing a manner of action or being. when combined in the late 16th century, the literal sense was "going through" a subject completely, which crystallized into its modern meanings of "comprehensive" and, by extension, "uncompromising" or "extreme" in one's approach. the logic of the word perfectly captures the idea of an action or quality that proceeds all the way through to its conclusion.

Structure: thorough + going - thorough: from old english thurh (through), functional role: adjectival base meaning "through and through, complete" - going: from old english gān (to go), present participle suffix -ing, functional role: forms an adjective meaning "proceeding in a specified manner"