n.understatement for rhetorical effect (especially when expressing an affirmative by negating its contrary)
"saying `I was not a little upset' when you mean `I was very upset' is an example of litotes"
同义词：meiosis
英汉双解大词典
litotes/ˈlaɪtəʊˌtiːz/
1.
N（名词）
understatement for rhetorical effect, esp when achieved by using negation with a term in place of using an antonym of that term, as in "She was not a little upset" for "She was extremely upset." 反语法