1 an agreement between two people or organizations who would not normally work together, usually for a bad purpose
an unholy alliance
2 [only before noun] informal bad and extreme :
3RR not holy, or not respecting what is holy
4 pleasure etc that you get from someone else's suffering :
He was taking an unholy delight in humiliating Sarah.
unholy amusement/delight/pleasure
He was taking an unholy delight in humiliating Sarah.