The term 'closed up' can be described by three words found in a crossword puzzle: SHUT, SILENT, and sealed. SHUT is a four-letter word meaning to close or fasten something securely. SILENT is a six-letter word meaning making no sound or noise. Sealed is also a six-letter word meaning to close or secure something tightly so that nothing can enter or escape. Together, these three words describe the concept of being closed up.