understatement
US /ˌʌn.dɚˈsteɪt.mənt/
UK /ˌʌn.dɚˈsteɪt.mənt/

1.
euphémisme, litote
the presentation of something as being smaller, worse, or less important than it actually is
:
•
To say it was difficult would be an understatement.
Dire que c'était difficile serait un euphémisme.
•
His calm reaction was a huge understatement of his true feelings.
Sa réaction calme était un énorme euphémisme de ses vrais sentiments.