Related Clues:

• Three in ---
• In ___ (aligned)
• In ___ (consecutively)
• Waiting one's turn
• Like some skates
• "... pretty maids all in ___"
• Three-in-___
• "Pretty maids all in ___"
• In -- (queued up)
• In -- (aligned)
• In ranks
• Congaing, e.g.
• '... pretty maids all in --'
• 'And pretty maids all in --'
• Strung out