The word "unspent" is a modern English compound formed by the productive combination of a native Germanic prefix and a verb of Latin origin. The prefix "un-," with its ancient Proto-Indo-European root ne- meaning "not," provides a straightforward negation. The core adjective "spent" originates from the Latin verb expendere, meaning "to weigh out" or "to pay," which itself derives from ex- ("out") and pendere ("to weigh"). The literal concept of weighing out money evolved into the general sense of using up resources. Therefore, "unspent" logically constructs its meaning as "not having been used up," directly preserving the semantic link from its constituent parts.

Structure: un (not) + spent (used up) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - spent: The past participle of the verb "spend," from Old English spendan (from Latin expendere, via Late Latin dispendere), meaning "to use up, to pay out." Here it functions as the core adjective meaning "used up."