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。