We have in Gn 39:7 an Imperative form, $IKBAH, lie down (you, male)! (an
alternative to $:KAB found in 2Sa 13:5)
In today Hebrew we find the common noun $IKBAH, layer, social stratum.
Apparently, an old Imperative form has become a feminine common noun today.
I'm looking for other analogous cases: do you know of some others?