IPA: //ˌʌnəˈsθɛtɪk//
KK: /ʌnəˈsθɛtɪk/
Not pleasing to the eye or not beautiful; lacking in visual appeal.
The building's design was considered unaesthetic by many architects.
Unaesthetic → It is formed from "un-" (meaning not) and "aesthetic" (from Greek "aisthesis", meaning perception or sensation). The word "unaesthetic" means not having a pleasing appearance or lacking beauty.
Think of 'not' ('un-') having a 'sense of beauty' ('aesthetic') — that's why unaesthetic means something that is not pleasing to look at.