IPA: //ʌnˈbjuːtɪfəl//
KK: /ʌnˈbjuːtəfəl/
Not pleasing to the eye; lacking beauty or attractiveness.
The unbeautiful building stood out among the elegant structures around it.
Unbeautiful → It is formed from "un-" (meaning not) and "beautiful" (from Old French *beauteux*, meaning possessing beauty). The word "unbeautiful" means not possessing beauty or lacking beauty.
Think of 'not' ('un-') combined with 'full of beauty' — that's why unbeautiful means lacking beauty.