put it mildly

put it mildly (third-person singular simple present puts it mildly, present participle putting it mildly, simple past and past participle put it mildly)

1. To state without exaggeration; to understate, to state in euphemistic terms.

   to put it mildly

   That's putting it mildly!

• to put it another way
• not to put too fine a point on it

• “to put it mildly”, in Merriam-Webster Online Dictionary
• “to put it mildly” in Longman Dictionary of Contemporary English, Longman.
• “to put it mildly” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.