The word "trusty" is a native English formation, combining the noun "trust" with the adjectival suffix "-y". The core element "trust" itself has a rich history, entering Middle English from Old Norse traust, which conveyed concepts of help, confidence, and firmness. This Norse term is related to the Old English trēowe (faithful, true), with both stemming from a Proto-Germanic root concerned with firmness and reliability. Therefore, "trusty" literally means "characterized by trust" or "full of reliability," a meaning that has remained consistent from its Middle English origins to its modern use describing a dependable person or object.

Structure: trust + y - trust: From Old Norse traust (help, confidence, firmness). Functions as the core semantic root. - y: From Old English -ig, a suffix forming adjectives meaning "characterized by; full of; having the quality of".