IPA: /ˈsædli/
KK: /ˈsædli/
In a way that shows sadness or regret.
She sadly watched her friend leave for another city.
Sadly → It is formed from "sad" (from Old English *sæd*, meaning filled with sorrow) and "-ly" (a suffix used to form adverbs). The word "sadly" means in a manner that is filled with sorrow or unhappiness.
Think of feeling 'sorrow' ('sad') and how the '-ly' turns it into an action or manner. So, when you say 'sadly', you are describing something done in a sorrowful way.