A pass between the Crissaegrim and Ered Gorgoroth (S/201). The meaning of the name is unclear, but it might be a compound of and “long” and ach¹ “neck”. Alternately, it could be the cognate of Q. (a)nacca “narrows, pass” (PE17/166); this second etymology was suggested to me by Matt Dinse in a 2022-07-26 Discord conversation.