Related Clues:

• Match-less?
• Without a match
• Like 7 or 11
• Offbeat
• Unmatched, like socks
• Lacking a partner
• Unmatched, as a sock
• Kooky or spooky
• Preternatural
• Very strange
• Eldritch
• Matchless, e.g.
• Unlike 666
• Strikingly odd
• Like all but one prime