IPA: /ˈsæd.nəs/
KK: /sæd.nəs/
The feeling of being unhappy or sorrowful.
She felt a deep sadness after her friend moved away.
Sadness → It is formed from "sad" (from Old English *sæd*, meaning sated or weary) and the suffix "-ness" (meaning the state or quality of). The word "sadness" refers to the state of being sad or the quality of feeling sorrowful.
Think of the word 'sad' which describes a feeling of sorrow, and remember that 'sadness' is the state of experiencing that feeling.