Also found in: Dictionary, Thesaurus, Medical, Legal, Encyclopedia.
To mess up or ruin something. The threat of a hurricane really fouled up our vacation plans! Boy, you really fouled up this report, and I don't have time to fix it right now.
messed up; ruined; tangled up. (Usually as fouled-up when attributive.) This is sure a fouled-up mess. You sure are fouled up, you know.
mod. messed up; ruined; tangled up. You sure are fouled up, you know.