n.

1. 间谍；密探[C]
   She liked the adventures of a spy.

   她喜欢间谍的冒险。

2. 暗中监视，暗中侦察[U]

vi.

1. 当间谍；暗中监视；刺探[（+on/upon/into）]
   We spied on the man.

   我们监视那个人。

vt.

1. 暗中监视；侦察出
   He sent out a party to spy the enemy.

   他派出一个小分队暗中监视敌人的行动。

2. 察觉，发现[O4]
   We spied a stranger hanging around the corner.

   我们发现一位陌生人在拐角处闲荡。

   He was the first to spy the triangle fin of a shark coming towards us.

   他第一个发现一条鲨鱼的三角形鳍向我们游来。

3. 仔细察看
   The visitors spied the exhibits at the fair.

   参观者细细察看展览会上的陈列品。

n.

1. a person employed by a government or other organization to collect and report secret information on an enemy or competitor.
2. a person who observes others secretly.

v.

1. be a spy.
   ▸ (spy on) observe furtively.
2. observe or notice.