understatement

Etymology

under- + statement or understate + -ment

noun

1. (uncountable, rhetoric) A figure of speech whereby something is made to seem smaller or less important than it actually is, either through phrasing or lack of emphasis, often for ironic effect.
   A master of understatement
2. (countable) An instance of such phrasing or lack of emphasis.
   Now that's an understatement.
3. An incomplete disclosure that intentionally withholds relevant information.