IPA: //ʌnˈtaɪmli//
KK: /ʌnˈtaɪmɪs/
Happening at an inappropriate or inconvenient time.
His untimely arrival disrupted the meeting.
This word originates from Middle English 'untimous', meaning untimely or inappropriate. The prefix 'un-' means not, and 'timous' (from Old French 'temo', meaning timely) refers to being timely or appropriate. Therefore, 'untimeous' describes something that is not timely or is inappropriate in timing.
Think of 'not' ('un-') being combined with 'timely' — this helps you remember that 'untimeous' means something that is not appropriate in timing.