The Japanese word 決意 meaning "Determination" and "Decision" is composed of the kanji決 (read ketsu) meaning "decide; fix; appoint" and 意 (read i) meaning "idea; mind; heart".
決意 is used both as a noun and a verb and is more along the lines of a "forceful decision" or a decision coming from one's mind as opposed to Determination (kesshin) which is more of a decision made from the heart. Though the two words are synonyms and are often used interchangeably.