IPA: //ʌnˈsɛntɪˌmɛntl//
KK: /ʌnˌsɛntəˈmɛntl/
Not showing or expressing strong feelings or emotions, especially in a way that is overly sentimental.
He took an unsentimental approach to the project, focusing only on the facts and figures.
Unsentimental → It is formed from "un-" (meaning not) and "sentimental" (from Latin "sentimentalis", meaning of feeling or emotion). The word "unsentimental" means not having or showing strong feelings or emotions.
Think of 'not' ('un-') having 'feelings' ('sentimentalis') — that's why unsentimental describes someone who doesn't show strong emotions.