"I am almost ready."
Translation:Je suis quasiment prêt.
"Quasiment" is an adverb meaning "almost". The real adverb is "quasi", directly coming from Latin with the same meaning (and pronounced by some as "kwazee"). It has been "Frenchized" to look like most French adverbs with the addition of the suffix -ment.
So it is not a modern word, but rather a word used in formal speech and writing.
"prêt(e)(s)" is an adjective = ready