The spelling of the word "rosest" is a bit tricky because it is an archaic form of the word "rousest." The IPA phonetic transcription for "rousest" is /ˈraʊstəst/, with the stress on the first syllable. The "-est" suffix is added to the base form "rouse," meaning to awaken or stir up. This form is no longer in common usage and has largely been replaced by the regular present tense form "rouses", but it is still used in some contexts where an archaic or poetic tone is desired.