sentinel
n. countable C2 Proficiency US //ˈsɛntənəɫ// UK //sˈɛntɪnəl// sen·tinel
n. a person whose job is to stand and watch for danger. They act like a guard to keep a place safe.
n. a person, such as a soldier or guard, stationed to keep watch and prevent unauthorized passage. Often used metaphorically in medical contexts to describe a cell or node that monitors for disease.
The sentinel stood quietly at the gate.
A lone sentinel remained on the castle wall, scanning the horizon for any sign of the approaching army.
In oncology, the sentinel lymph node is the first one reached by metastasizing cancer cells, serving as a crucial indicator for the extent of the disease's spread.
Usage
Often used in the phrase 'to stand sentinel', meaning to act as a guard.