n. The action of not allowing, or of withdrawing allowance.
the GNU version of the Collaborative International Dictionary of English
n. The act of disallowing; refusal to admit or permit; rejection.
The Century Dictionary and Cyclopedia
n. Disapprobation; refusal to admit or sanction; prohibition; rejection.
Word Usage
"The disallowance equal to 7.5% of adjusted gross income is a high hurdle, but those who qualify shouldn't overlook all possible expenses, listed in IRS publication 502 ."