IPA: //ʌnˈhɛlθiər//
KK: /ʌnˈhɛlθiər/
This word describes something that is more harmful to health compared to something else.
Eating junk food is unhealthier than eating fruits and vegetables.
Unhealthier → It is formed from the prefix "un-" (meaning not) and the root "healthy" (from Old English *halig*, meaning whole or sound) combined with the comparative suffix "-er" (indicating a higher degree). The word "unhealthier" means in a state that is not healthy to a greater extent than something else.
Think of 'not' being added to 'healthy' — that's why 'unhealthier' means something that is not healthy to a greater degree.