intransitive verb
Definition: To secretly watch or listen to someone or something, often to gather information.
Example: He likes to spy on his neighbors to see what they are doing.
noun
Definition: A person who secretly collects information about others, often for a government or organization.
Example: The spy gathered important information about the enemy's plans.
transitive verb
Definition: To watch or observe someone secretly, often to gather information.
Example: The detective decided to spy on the suspect to find out more about his activities.