not a few 的意思是“不少”，也就是“很多”“相当多”“颇有一些”的意思。如：

Our achievements are the main thing in our work, and yet there are not a few shortcomings and mistakes. 我们的工作中成绩是主要的，但缺点和错误也还不少。

又如：

Not a few students have gone home. 不少学生已经回家

Last night not a few of the students were present. 昨晚有不少学生出席。

Not a few of my friends are vegetarian. 我朋友中不少人吃素。

Both students have made not a few experiments on electricity. 这两个学生都做了不少电学实验。

类似地，not a little的意思是“不少”“相当多”（用作形容词时）。如：

I am so sorry to give you not a little trouble. 真抱歉给你添了这么多麻烦。

not a little若用作副词，则表示“不是一点儿”“相当”“非常”。如：

He was not a little surprised. 他极为惊讶。

She was not a little worried about the expense. 她对那笔开支相当苦恼。