decade-old

The compound adjective "decade-old" is a modern English formation that transparently combines two distinct and ancient roots. The first element, "decade," traces back to the Greek deka (ten), a numeral with a clear Proto-Indo-European origin (déḱm̥t), which entered English via Latin and French to signify a period of ten years. The second element, "old," descends from the Proto-Germanic aldaz, from the PIE root h₂el- (to grow, nourish), evolving in Old English to denote advanced age or duration. The compound's logic is purely syntactic, directly linking a quantified timeframe ("decade") with the adjectival state of existence ("old") to describe anything that has reached a ten-year age.

Structure: decade (ten years) + old (aged) - decade: From Latin decas, from Greek dekas (a group of ten), from deka (ten). The functional role is to denote a period of ten years. - old: From Old English eald, ald (aged, ancient, mature). The functional role is to denote the state of having existed for a specified time.