Freshen comes from fresh (from Old English fersc, 'unsalted, pure', reinforced by Old French freis) + the verb-forming suffix -en. The suffix is part of the word's derivational shape, marking the final grammatical or semantic role while the base supplies the central meaning. As a verb, it means "to make or become fresh, cleaner, or more invigorated", so the modern sense keeps the older action or relation visible. Relevant historical forms include Old English fersc and Proto-Germanic *friskaz. Derivative forms include freshened, freshener, freshening; related words include fresh, freshly, freshness.