Is Smoothen a Real Word?

to make or become smooth.

Does smooth have an E?

Smooth is the only correct version of this verb, but how can we remember this fact? Smoothe has an extra E. Since it is an error, and both smoothe and error contain the letter E, it will be an easy task to remember that smoothe is an error.

Is smoothen correct?

Meaning of smoothen in English. to smooth : Rub the outside of halved coconut shells with sandpaper to smoothen the surface.