The compound "year-ago" is a modern English formation that transparently combines two native English elements. "Year" has a deep Germanic lineage, tracing back to a Proto-Indo-European root meaning "year, season." "Ago" originates from the Old English verb 'āgān', meaning "to go away, pass." The compound's logic is entirely literal, denoting something that belongs to a year that has "gone by" or passed. It functions as a fixed attributive adjective, succinctly packaging the temporal concept of "in the past year" into a single grammatical unit, reflecting English's capacity for efficient compounding.

Structure: year (time period) + ago (past) - year: From Old English 'gēar', meaning a cycle of seasons, a year. Germanic origin. - ago: From Middle English 'ago', 'agon', meaning past, gone by. From Old English 'āgān', to pass away, composed of 'ā-' (away, off) and 'gān' (to go).