Part of speech: adverb1 slightly; not very much:
mildly surprised / irritated / interested * Those figures are mildly encouraging, but we need faster progress.
2 in a gentle manner:
'I didn't mean to upset you' he said mildly.
IDIOMS
to put it mildly (spoken) used to show that what you are talking about is much more extreme, etc. than your words suggest:
The result was unfortunate, to put it mildly (= it was extremely unfortunate). * To say I'm disgusted is putting it mildly.
