Humans have been making objects out of wood since before there even was an English language, but the adjectival use of "wood" didn't come into being until the 14th century, and "wooden" didn't appear until the 16th. (The word wood has ancient roots, but it originally existed only as a noun.) In Middle English, the adjective of choice was "tree" or "treen," as in a "tree vessel" or "treen shoes." "Treen" in turn came from the Old English word trēowen, from the noun "trēow" ("tree") and the suffix -en, which was used to indicate that something was composed of a certain material. As far as we know, no one ever used "treen" figuratively to describe things that are stiff as a board, but "wooden" was put to broader use soon after it was first recorded.