Possible Clues:

• Trees in bits in tin, not in principal
• Not the principal way to get in come
• Money paid on deposit account or loans
• Some Schedule B income
• What is to be paid on loan, out of curiosity?
• Something gotten on principal
• Pastime
• It can be absorbing, but not a principal extent
• That's not the principal thing at all
• Money earned by money in deposit account