The Japanese word 決心 meaning "Determination" and "Resolution" is composed of the kanji決 (read ketsu) meaning "decide; fix; appoint" and 心 (read shin) meaning "heart; mind; spirit".
決心 is used both as a noun and a verb and is more along the lines of a "felt decision" or a decision coming from one's heart or soul as opposed to Determination (ketsui) which is more of a decision made from the mind or logic. Though the two words are synonyms and are often used interchangeably.
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.