sentineln.[F. sentinelle (cf. It. sentinella); probably originally, a litle path, the sentinel's beat,, and a dim. of a word meaning, path; cf. F. sente path. L. semita; and OF. sentine, sentele, senteret, diminutive words. Cf. Sentry.]1. One who watches or guards; specifically (Mil.), a soldier set to guard an army, camp, or other place, from surprise, to observe the approach of danger, and give notice of it; a sentry.()The sentinels who paced the ramparts. (Macaulay.)2. Watch; guard.(Bacon.)3. (Zol.) A marine crab (Podophthalmus vigil) native of the Indian Ocean, remarkable for the great length of its eyestalks; -- called also sentinel crab.()v. t.1. To watch over like a sentinel.(Sir W. Scott.)2. To furnish with a sentinel; to place under the guard of a sentinel or sentinels.()