Related Clues:

• Stylebook subject
• It's done again and again
• Chewing one's nails, e.g
• Dictionary subject
• States how old one is — it's the custom
• Electric bill figure
• Hard thing to break
• Acquired pattern of behaviour
• Linguistics topic
• Employment on Canadian border rising, for example
• Customary habit
• Practice one learned after university
• American takes time to establish tradition
• Treatment of uranium appearing wise?
• With heroin, just some can cause addiction