Capping a threadless pipe

Hello,
I have a house from 1883 and I am trying to convert a bathroom back into a walk-in closet. The house was built before plumbing and when plumbing was installed they turned an existing closet into a full bathroom. Since we converted a small bedroom into a bathroom and plan to turn the old bathroom back into a closet. We ran new piping to new bathroom and the project was completed in March.

Now I am trying to decipher the existing labyrinth of piping that runs from the basement to the second floor and then splits between a parlor sink in one bedroom and the old bathroom. Believe me when I say it is not a straight line. I was able to cap the drains and hot water but made a mistake when it came to capping the cold water line. The line had a third split that I did not see and I accidentally cut the wrong side of the line. Now I'm left with a pipe that I need to cap with no threads or no option thread the line. Is there a way to cap the line without the threads? The valve in the basement is holding and we do not have any plans to use the line but I would feel better if it did have some sort of cap. Any help anyone can provide would be greatly appreciated.

Why not cut off the line in the basement and cap it at the valve or remove the valve and cap it there.

For one joint, you can use a ratchet threader.

For once sharkbites can't come to the rescue.

cap

Either thread the pipe, or remove it to the point where you can use a cap or plug.

My thought is that while you are in there, it is probably time to replace the galvanized pipe with something more modern, too. Then threading becomes a non-issue.