There are several synonyms for the word "eavesdrops", including: listens in, overhears, spies, snoops, and surveils. Each of these words implies a certain level of secrecy or surreptitiousness when listening to conversations or gathering information. To "listen in" suggests that someone is surreptitiously tuning in to a conversation, while "overhears" implies that the person accidentally heard something they weren't meant to. "Spies" and "snoops" both suggest a more active and voluntary effort to gather information, while "surveils" implies a more technological and less personal approach to monitoring conversations. Ultimately, all of these words describe ways in which someone can gather information without the knowledge or consent of the people they are observing.