Basis for a write-off, perhaps

TAXASSET

This financial item can reduce taxable income and appears on balance sheets.

The clue hints at something used to reduce taxable income, which is often referred to as a "write-off." The answer "TAXASSET" combines "tax" with "asset," where an asset can be a financial resource that qualifies for tax deductions. The wordplay lies in interpreting "write-off" as a tax-related term and recognizing "asset" as a key component in tax accounting.