DICT.TW Dictionary Taiwan

 Sen·ti·nel, n.
 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. [Obs.] “That princes do keep due sentinel.”
 3. Zool. A marine crab (Podophthalmus vigil) native of the Indian Ocean, remarkable for the great length of its eyestalks; -- called also sentinel crab.