Sentinel

Webster's Practical Dictionary- A Practical Dictionary of the Englih Language · 1884 · p. 386

sen'tY-nel, n. (Mil.) A soldier set to watch or guard an army, camp, etc., from surprise. — Sen'try, -trY, n. A soldier on guard; sentinel; guard watch; duty of a sentinel. — Sen'try-box, n. A box to cover a sentinel at his post, and shelter him from the weather.