IPA: /ʌnˈhæpiər/
KK: /ʌnˈhæpiər/
Feeling or showing a greater degree of sadness or dissatisfaction than usual.
After hearing the bad news, she felt unhappier than before.
Comparative: unhappier
Superlative: unhappiest
Unhappier → It is formed from "un-" (meaning not) and "happy" (from Old English "hap", meaning luck or fortune) and the comparative suffix "-er" (indicating a higher degree). The word "unhappier" means in a state of being not happy to a greater extent than before.
Think of 'not' ('un-') being added to 'happy' — so when someone is 'unhappier', they are not just unhappy, but even more so.