hatbrim is a compound of hat (Old English hæt, from Proto-Germanic *hattuz) and brim (Middle English brim 'edge, border, water's edge'). Morphologically, the word is best read through the components named in the history, with the modern spelling preserving a compound structure rather than a single unanalyzable stem. In present English, the noun sense is "the projecting edge or rim of a hat", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as hat and brim. Its semantic neighborhood includes brim, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English hæt.