IPA: /ˌʌnˈdɪpləˌmætɪk/
KK: /ʌnˈdɪpləˌmætɪk/
Not showing the ability to deal with sensitive matters in a tactful way; lacking in diplomacy or tact.
His undiplomatic remarks during the meeting upset many of the attendees.
Undiplomatic → It is formed from "un-" (meaning not) and "diplomatic" (from Greek "diplomatikos", meaning relating to diplomacy). The word "undiplomatic" means not relating to diplomacy or lacking the tact typically associated with diplomatic behavior.
Think of 'not' ('un-') being combined with 'diplomatic' to remember that 'undiplomatic' describes someone who lacks the tact or finesse usually found in diplomatic situations.