IPA: //ʌnˈtæktfəl//
KK: /ʌnˈtæktfəl/
Not showing sensitivity or consideration in dealing with others; lacking tact.
His untactful remarks upset many people at the meeting.
Untactful → It is formed from "un-" (meaning not) and "tactful" (from Latin "tactus", meaning touch, and the suffix "-ful", meaning full of). The word "untactful" means not full of tact or sensitivity in dealing with others.
Think of 'not' ('un-') being combined with 'full of touch or sensitivity' ('tactful') to remember that 'untactful' describes someone who lacks sensitivity in their interactions.