Related Clues:

• Slaving away
• Squabbling
• Butting heads
• Engaged
• Working away
• Going ___ tooth and nail
• Keep ___ (persevere)
• On the job
• Wrangling
• Arguing loudly
• Feuding
• Persisting
• Having one's nose to the grindstone
• Keep -- (persist)
• Locking horns