Related Clues:

• Fortitude
• It bollixes up the machinery
• Chew like a beaver
• Erode
• Chew, like a beaver
• Gumption
• Stick-to-it-iveness
• Doggedness
• Nerve
• Eat away at
• Mettle
• Resolve
• Chew on, as a bone
• Staying power
• Act like a beaver