IPA: /ˌɪnəˈpɔːrtjuːn/
KK: /ɪnˈɑːpərˌtun/
Not suitable or well-timed; occurring at a bad time.
His arrival was inopportune, as the meeting had just ended.
Inopportune → It is formed from "in-" (meaning not) and "opportunus" (from Latin, meaning suitable or favorable). The word describes a time or situation that is not suitable or favorable for something to happen.
Think of 'not' ('in-') being combined with 'suitable' ('opportunus') to remember that 'inopportune' refers to something that is not suitable or favorable.