BT BM 104b(33) :כחשה דארעא‏ :
See the entire entry for kḥāš, kḥāšā v.n. weakening

BT BM 104b(33) :מנכי ליה כחשה דארעא‏ : the (tenant farmer) deducts (the diminished value lost from) the deterioration of the field (by planting wheat) from it [i.e. the rent]
See the entire entry for nky vb. to damage