Affixes

For the most part, words in ‑our are variants of those in ‑or (see ‑or¹ and ‑or²). However, there are some that derive from a variety of other sources, such as endeavour (late Middle English, in the sense ‘exert oneself’; from the phrase put oneself in devoir, do one's utmost), harbour (Old English herebeorg, shelter, refuge), neighbour (Old English, from nēah, near, plus gebūr, inhabitant, peasant, farmer), and parlour (Anglo-Norman French parlur, place for speaking, from Latin parlare, speak). All these are usually written ‑or in American English.