1. 不充分如实的陈述；轻描淡写的说明
If you say that a statement is an understatement, you mean that it does not fully express the extent to which something is true.

2. 轻描淡写；重事轻说；淡化
Understatement is the practice of suggesting that things have much less of a particular quality than they really have.

1. a statement that is restrained in ironic contrast to what might have been said