/ ˈædə(r); NAmE / noun
a small poisonous snake, often with diamond-shaped marks on its back. Adders are the only poisonous snakes in Britain.
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WORD ORIGIN
Old English nædre serpent, adder , of Germanic origin; related to Dutch adder and German Natter . The initial n was lost in Middle English by wrong division of a naddre ; compare with apron and umpire .