n. (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors
n. a secret watcher; someone who secretly watches other people
v. watch, observe, or inquire secretly
v. catch sight of; to perceive with the eyes
n. 间谍, 侦探, 侦察
vt. 侦察, 找出, 发现
vi. 做密探, 侦查