זאָדיק
'behind, backside'

ETYMOLOGY

Formally it could come either from Old Czech or Polish, but Beider thinks it belongs to a group of butcher's terms borrowed from Old Czech. He suggests that the root vowel (protovowel A₂, from a long /aː/) stems from Czech á [although the vowel in Czech zadek appears to be short]
Old Czech zadek; Polish zadek.