A soldier stationed to keep guard.

A form of watch or guard in a general sense.

निगरानी

English Usage: The sentry's duty was to ensure no unauthorized personnel entered the area.

Hindi Usage: पहरेदार का काम यह सुनिश्चत करना था कि कोई अनधिकृत व्यक्ति क्षेत्र में प्रवेश न करे।

To act as a guard or watch over something.

पहरा देना

English Usage: They were sentrying the perimeter during the night.

Hindi Usage: वे रात के समय perimeter की पहरा दे रहे थे।