IPA: /ˈsædər/
KK: /ˈsædər/
Feeling or showing sorrow or unhappiness to a greater degree than usual.
After hearing the bad news, she felt even sadder than before.
Comparative: sadder
Superlative: saddest
Sadder → It is formed from "sad" (from Old English *sæd*, meaning filled with sorrow) and the comparative suffix "-er" (meaning more). The word "sadder" means more filled with sorrow than another state or person.
Think of someone who is 'more filled with sorrow' — that's what 'sadder' means.