discharge 语气较重，指有理由的解雇，含几乎不再复用的意味。
dismiss 正式用词，是这组词中语气最轻的一个词，一般只有从上文才能看解雇的原因或理由。
fire 口语用词，多指被断然地突然解雇，其行动犹如开枪一样干净利落。
参考例句
1. He dismissed the story as mere rumor. 他认为那种传闻纯属谣言而拒绝考虑。
2. When to dismiss a incompetent subordinate? How? 如何开除一个不称职的下属？
3. Either you improve your work or I shall dismiss you. 要么你改进你的工作，否则我就解雇你。
英英解释
v.
1. bar from attention or consideration
2. cease to consider; put out of judicial consideration
3. stop associating with
4. terminate the employment of
5. end one's encounter with somebody by causing or permitting the person to leave
6. declare void
