Related Clues:

• Act of respect
• 'There -- to be a law!'
• Strange thing
• Required task
• Be obliged (to)
• "You __ to know!"
• Certain tax
• Airport patrons often avoid it
• Should, with "to"
• Job description detail
• Official obligation
• Obligation, responsibility
• Should, had, better
• Had better
• Be logically necessary