What does "sentinel" mean?

Sentinel: Watch; guard. [Obs.] "That princes do keep due sentinel." Bacon.

Additional senses

  1. 2.(Zoöl.) A marine crab (Podophthalmus vigil) native of the Indian Ocean, remarkable for the great length of its eyestalks; -- called also sentinel crab.
  2. 3.To watch over like a sentinel. "To sentinel enchanted land." [R.] Sir W. Scott.
  3. 4.To furnish with a sentinel; to place under the guard of a sentinel or sentinels.

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