verb/mɛ.tʁə sa tɛt a ku.pe/
to bet one's life that, to bet one's boots that, to bet one's bottom dollar that (to be absolutely sure that)
“J'en mettrais ma tête à couper.”
Synonyms: mettre sa main à couper, donner sa main à couper, mettre sa main au feu
Compare Polish dać sobie głowę uciąć.