noun
guard; sentry; security soldier
A soldier assigned to guard duty, such as at a base, building, or checkpoint.
基地の入り口には警備兵が立っていた。
A guard was standing at the entrance to the base.
衛兵 is a more general term for a guard or sentry, often used for ceremonial or palace guards.
Compound of 警備 (けいび, 'security, guard') and 兵 (へい, 'soldier').