Spy out is a common phrase that refers to the act of obtaining information secretly or by stealth. Some synonyms for spy out include investigate, scout, probe, explore, scrutinize, inspect, observe, monitor, and surveil. These words all involve methods of gathering information, but may differ in terms of the degree of secrecy involved. For example, monitoring may involve open observation, while spying out suggests a more surreptitious approach. Regardless of the synonym used, the act of spying out can have negative connotations, so it is important to use these words with care and in contexts where such activities are appropriate and ethical.