一个既可以作名词也可以作动词的单词,在句子里面只能有一种词性,即名词,或者动词.
比如work,做动词时：he works hard every day.
做名词时：i have a lot of work to do.
而动名词在句子里既有名词的特性（即在句子里充当主语或者宾语）,又有动词的特性（即可以被副词修饰）,比如：working hard every day makes him tired.在这个句子里,working hard every day 做主语,而working 可以有动词的特性,可以有hard 修饰它.
希望对你有用.