difficult
词根词缀：
difficult adj. 困难的
dif 不，否定 + fic 做 + ult → 不好做 → 困难的
diffident adj. 自卑的
dif 不，否定 + fid 相信 + ent 关于…的 → 不相信〔自己〕的 → 自卑的
differ v. 不同
dif 分开 + fer 带来 → 分开带来 → 不同
difference n. 不同
differ的名词
diffluence n. 分流；溶解
dif 分开 + flu 流 + ence 表状态 → 分开流 → 分流
diffuse v. 撒播
dif 分开 + fus 流 + e → 使散开流 → 撒播
数据来源：新东方英语词汇速记大全
相关例句：
The problem will not be difficult to solve, if properly handled.
如处理得当，问题不难解决。
The people have asserted their power and that will be very difficult to reverse.
人民已经维护了其当家作主的权力，这将难以改变。
Difficult circumstances can temper one's will.
艰苦的环境能磨炼人的意志。
How to improve the quality of products was a difficult problem to him.
如何提高产品质量对他来说可是个难题。
The vowel in words like 'my' and 'thigh' is not very difficult.
单词my和thigh中的元音并不难发。
It's not difficult to get money for research or at least it's not always difficult
争取到研究资金并不难，起码不总是那么难。