interannual

The word "interannual" is a modern scientific compound formed within English by combining two established Latin-derived elements. The prefix "inter-", from Latin inter meaning "between, among", has been a productive prefix in English since the Middle English period, borrowed via Old French. The root "annual" descends from Latin annuālis, itself from annus (year), a word of Proto-Indo-European origin (h₂et-no-, likely related to going, denoting the "going" or passage of time). The logical construction is perfectly transparent: "inter-" (between) + "annual" (pertaining to years) directly yields the meaning "occurring between years," used to describe phenomena, variations, or comparisons that span multiple yearly cycles.

Structure: inter (between) + annual (yearly) - inter: A prefix of Latin origin, meaning "between, among". It functions as a locative prefix in this word. - annual: An adjective of Latin origin (from annus meaning "year"), meaning "yearly" or "occurring every year". It functions as the core root.