IPA: //ʌnˈfæstɪdiəs//
KK: /ʌnˈfæstɪdɪəs/
Not being very careful about details or not being picky about things.
He was unfastidious in his approach to cleaning, often leaving things messy.
Unfastidious → It is formed from "un-" (meaning not) and "fastidious" (from Latin "fastidiosus", meaning difficult to please or overly particular). The word "unfastidious" means not being overly particular or difficult to please.
Think of 'not' ('un-') being combined with someone who is 'difficult to please' ('fastidious') — that's why unfastidious means someone who is easygoing or not picky.