1A land feature used to take bearings at sea, frequently in order to demarcate fishing grounds; a seamark. Also (in extended use): any mark or distinguishing feature facilitating orientation on land or at sea.
2A bearing, course, direction; frequently with take. Also: a measurement taken from a mark (rare). Chiefly in plural (occasionally with singular agreement).
3 figurative A distinctive mark or sign; an indication; a point of reference.
Late Middle English (in an earlier sense). Partly from early Scandinavian (compare Old Icelandic mið middle, mark, fishing bank indicated by landmarks on shore (Icelandic mið middle, landmark, fishing ground, goal), Norwegian (Nynorsk) mid fishing ground, Swedish regional med, me, mej bearings, orientation at sea in respect of landmarks, Danish med mark, target, goal) from the Germanic base of mid; and partly (in later use) from meith.