n. 25B6; noun a foreign spy : SECRET AGENT, intelligence agent, double agent, counterspy, mole, plant, scout; informal snooper; N. Amer. informal spook; archaic intelligencer.
25B6; verb
he spied for the West : BE A SPY, gather intelligence, work for the secret service; informal snoop.
investigators spied on them : OBSERVE FURTIVELY, keep under surveillance/observation, watch, keep a watch on, keep an eye on.
she spied a coffee shop : NOTICE, observe, see, spot, sight, catch sight of, glimpse, make out, discern, detect; informal clap/lay/set eyes on; poetic/literary espy, behold, descry.