IPA: //ʌnˈdʒɛntəl//
KK: /ʌnˈdʒɛntəl/
Not kind or mild; harsh or severe in manner or action.
His ungentle words hurt her feelings.
Ungentle is formed from "un-" (meaning not) and "gentle" (from Old French *gentil*, meaning noble or well-born). The word describes someone who is not noble or well-mannered, hence lacking gentleness.
Think of 'not' ('un-') being added to 'gentle' — this helps you remember that ungentle means someone who is not gentle or lacks kindness.