Definition of: whack

(hwak) v.t. & v.i.
1. Colloq. To strike sharply; beat; hit.
2. Slang To share: often with up.
3. Slang To drive (mules or oxen).
—noun
1. Colloq. A sharp, resounding stroke or blow.
2. The noise made by such a blow.
3. Slang A share; portion.
3. Slang A turn; a chance; a try.
—to have a whack at Slang
1. To give a blow to.
2. To have a chance or turn at; to have a chance to try.
—out of whack Slang Out of order. [? Var. of THWACK]