To come or go into: The train entered the tunnel. To penetrate; pierce: The bullet entered the victim's skull. To introduce; insert: She entered the probe into the patient's artery. To become a participant, member, or part of; join: too old to enter the army; entered the discussion at a crucial moment. To gain admission to (a school, for example). To cause to become a participant, member, or part of; enroll: entered the children in private school; entered dahlias in a flower show. To embark on; begin: With Sputnik, the Soviet Union entered the space age. To make a beginning in; take up: entered medicine. To write or put in: entered our names in the guest book; enters the data into the computer. To place formally on record; submit: enter a plea of innocence; enter a complaint. To go to or occupy in order to claim possession of (land). To report (a ship or cargo) to customs. To come or go in; make an entry: As the President entered, the band played "Hail to the Chief.\u201d To effect penetration. To become a member or participant. enter into To participate in; take an active role or interest in: enter into politics; enter into negotiations. enter into To become party to (a contract): The nations entered into a trade agreement. enter into To become a component of; form a part of: Financial matters entered into the discussion. enter into To consider; investigate: The report entered into the effect of high interest rates on the market. on To set out on; begin: We enter on a new era in our history. on To begin considering; take up: After discussing the budget deficit, they entered on the problem of raising taxes. on To take possession of: She entered upon the estate of her uncle.