IPA: /ʌnˈɔːrnəˌmɛntɪd/
KK: /ʌnˈɔrnəˌmɛntɪd/
Not decorated or embellished; plain in appearance.
The room was unornamented, with only the bare essentials for furniture.
Unornamented → It is formed from "un-" (meaning not) and "ornamented" (from Latin "ornamentum", meaning decoration). The word "unornamented" means not decorated or lacking adornment.
Think of 'not' ('un-') having any 'decoration' ('ornamented') — that's why unornamented means lacking decoration.