Possible Clues:

• Without exaggeration
• "And that's an understatement" (... first 2 letters + the last 3)
• Not to exaggerate
• Task for a Benedictine monk?
• Utter minimum, putting it mildly
• What Trappists are told, putting it mildly!
• To put it mildly
• Wild
• In reality it's more so!
• The ambition of the reluctant speech-maker : not to exaggerate