penult, penultimate
How common are these words? What alternatives you use as a replacement for these words?

Question

Answer

penult= a noun meaning the syllable preceding the final one. in a word
penultimate= an adjective meaning next to last.
Neither word is used very often except when you are talking about linguistics.

Answer

penultimate is not used very often but it is used, penult I don't think I've ever heard or seen used.
"Next to last" is the most common replacement.