Was "rhythm" once spelled "rhythmn"?

I distinctly have the memory of my first grade teacher and the classroom we were in…and the chalkboard… and her telling us not to forget the “n” just because it was silent.

What happened?

I just searched the internet for the answer, no luck. It seems I was not the only one who was told this as a child. Many people are wondering what I’m wondering. Rhythm just looks truncated to me…