underwithhold

verb (used with object), un·der·with·held, un·der·with·hold·ing.

1. to withhold too little.
2. to deduct (withholding tax) less than the necessary amount.

verb (used without object), un·der·with·held, un·der·with·hold·ing.

3. to withhold oneself too little.
4. to deduct less withholding tax than necessary.