The adjective 'vault-like' is a modern English compound formed by a straightforward morphological process. Its first element, 'vault', traces a journey from the Latin verb volvere, meaning "to roll or turn," through Vulgar Latin and Old French, where it came to denote an arched roof—a shape conceptually linked to a rolling or turning surface. The second element, the suffix '-like', is of ancient Germanic origin, ultimately from a Proto-Germanic root for "body" or "form," used to create adjectives indicating resemblance. Thus, the compound's logic is transparent: it literally means "having the form or characteristics of an arched structure," directly connecting the ancient concept of a curved form to the modern descriptive sense of something cavernous, secure, or arched.

Structure: vault (noun) + like (adjective-forming suffix) - vault: From Middle English voute, from Old French voute, volte, from Vulgar Latin volvita, a derivative of Latin volvere ("to roll, turn"). In this compound, it functions as the nominal root specifying the object of resemblance. - like: From Middle English -lik, from Old English -līc ("body, form, like"), from Proto-Germanic -līkaz ("having the form of, body"). It functions as a suffix forming adjectives meaning "having the characteristics of; similar to."