Related Clues:

• See 20 Across
• Single-file
• Having no depth, in brief
• Linear, briefly
• Having only length
• Undeviating
• Linear, unlike holographic images
• Came first
• Aced
• Like a line, for short
• Way to organize all your ducks?
• Flat, for short
• ___ as an arrow
• Lined up single-file
• Lacking width and depth, briefly