Question about the -mu suffix

I'm currently learning Japanese and I'm curious if there exists a verbal suffix -mu or if it's just coincidence.
For example, 'kanashii' means 'sad' and 'kanashimu' means 'to feel sad'
And 'tanoshii' means 'pleasant' and 'tanoshimu' means 'to enjoy'.
So yeah, I was curious whether there was a verb forming suffix '-mu' which was only productive in certain cases, or whether it's just coincidence.