Strict; stringent; secure — careful and thorough measures taken to prevent problems, or strong security/precautions.
重要書類は厳重に保管してください。
Please keep important documents under strict custody.
空港では厳重な手荷物検査が行われている。
Strict baggage checks are being conducted at the airport.
違反者には厳重な処分が下された。
Severe penalties were imposed on the violators.