The phrase "listen stealthily" means to listen in secret or without being noticed. There are many different ways to express this action through synonyms. Some alternative phrases include: eavesdrop, spy on, snoop, peep, monitor, overhear, or secretly keep an ear out. Each of these phrases carries a slightly different connotation. For example, eavesdropping often implies that the listener is intentionally trying to hear something private, while monitoring implies a more passive, systematic approach to listening. No matter which synonym is used, it's clear that listening stealthily is a secretive and often frowned upon action.