Related Clues:

• Unique
• Sole
• Incomparable
• There's nothing like it
• Unrepeated event
• Not to be repeated, as a performance
• Not to be repeated
• Made as single article, not repeated
• Not repeated or reproduced, a single thing
• Not reproduced or repeated
• Not repeated, being a single event or object
• Made or done as a single thing, not repeated
• A single event, not reproduced or repeated
• Not repeated - singular
• O'Neill might thus be ill in a singular manner