Related Clues:

• Slipper without a back
• Army's mule, e.g.
• Beast of burden
• Part of a wagon train
• Pack animal
• Lucky charm
• One who won't budge
• Chimney output
• Stubborn sort
• Plodding sort
• Navy's goat, e.g.
• Plow puller
• Princeton's Tiger, e.g.
• Paid smuggler
• Donkey