Bash/zsh: Undo erase backwards (ctrl+w)

Undo it's like this : ctrl + _

This below shortcut key does the job of undo the erased string by ctrl+w,

ctrl+y

It's ctrl + /

ctrl + y pastes what's in the buffer, the buffer get's filled by things like ctrl + w, you can paste it in different places multiple times, so it's not an "undo". ctrl + / does undo every action, you can hit ctrl + / multiple times to undo every action.