sen·ti·nel 
/ˈsɛntənəl/ noun
plural sen·ti·nels /ˈsɛntənəl/ noun [count] : sentry
▪ armed sentinels — sometimes used figuratively ▪ The trees stand sentinel [=stand in a row like soldiers] on the cliffs.
▪ armed sentinels — sometimes used figuratively ▪ The trees stand sentinel [=stand in a row like soldiers] on the cliffs.
