Related Clues:

• Figure
• Digit
• Number
• It may be Roman or Arabic
• It can be Roman
• 1, for one
• 3 or III, e.g.
• X, at times
• I, for one
• XVI, for one
• XII, for one
• One is one
• Inclusion in safer passwords
• X, e.g.
• 1, 2, 3, for instance