BT Er 76b(7) :כל אמתא בריבועא אמתא ותרי חומשי באלכסונא‏ : the diagonal in every square of (a side of ) one cubit, is one and two-fifths cubits
See the entire entry for ˀlkswn n.m. diagonal

BT Er 76b(7) :שיבסר נכי חומשא‏ : seventeen less one fifth (i.e., sixteen and four fifths)
See the entire entry for nəḵē adj. injured; defective