The Hebrew Word for Passover

The word Passover is used as a noun to describe the event itself, but that noun comes from a verb. If you look in Exodus chapter 12, verses 12 and 13, you get the appearance of the word Passover for the first time. There's a little puzzle here. This is God speaking to the Israelites. I will pass through the land of Egypt that night. But then when he comes to a house that has the blood, he's going to passach. And when he passachs, there's no strike upon that house.