The two Hebrew nouns ish and ishshah were originally employed to
designate the “male and female” of human beings, but were afterwards
applied to the “male and female” of the other species of the animal
creation. For instance, we read, “Of every clean beast thou shalt take
to thee by sevens,” ish ve-ishto (Gen. vii. 2), in the same sense as
ish ve-ishshah, “male and female.” The term zakar u-nekebah was
afterwards applied to anything designed and prepared for union with
another object. Thus we read, “The five curtains shall be coupled
together, one (ishshah) to the other” (aḥotah) (Exod. xxvi. 3).
It will easily be seen that the Hebrew equivalents for “brother and
sister” are likewise treated as homonyms, and used, in a figurative
sense, like ish and ishshah.