sentinel
noun
[ ˈsɛntɪn(ə)l ]
• a soldier or guard whose job is to stand and keep watch.
• "soldiers stood sentinel with their muskets"
• an indicator of the presence of disease.
• "a sentinel surveillance programme for influenza"
sentinel
verb
• station a soldier or guard by (a place) to keep watch.
• "a wide course had been roped off and sentinelled with police"
Origin:
late 16th century: from French sentinelle, from Italian sentinella, of unknown origin.
