successful词性是形容词
释义：something that is successful achieves what it was intended to achieve.Someone is successful achieves what they intended to achieve.有成效的
例句 How successful will this new treatment be? 这种新疗法将会有多大成效?
successful的反义词是unsuccessful
释义：Something that is unsuccessful does not achieve what it was intended to achieve. 不成功的
例句：His efforts were unsuccessful.他的努力没有成功。
successful的反义词
successful是成功的意思所以反义词是失败可以是fail还有unsuccessful这个词，也是不成功，失败的意思可以使用
