Many words once in common use are rarely seen today, but prefixes and suffixes have kept the root alive:
COUTH meant known, familiar. So UNCOUTH is bad-mannered, strange.
RUTH meant to rue, to feel compassion for. If you’re RUTHLESS, that compassion is gone.
HAP meant lucky. Now HAPLESS means unlucky or incompetent.
KEMPT meant combed, tidy. UNKEMPT implies a person is sloppy or messy.
FECK meant effective, strong, so FECKLESS is weak or ineffective.
GRUNTLE meant to complain . DISGRUNTLE, however, isn’t an opposite; it’s an intensifier.
WIELDY meant agile. (You saw all those wieldy athletes at the Olympics, right?) UNWIELDY is clumsy, awkward.
RULY meant well behaved, obeying the rules. UNRULY behavior is rarely tolerated.