uncousinly

/ʌnˈkʌzɪnli/
adjective
  1. Not appropriate or typical of a cousin; not showing the kindness, loyalty, or closeness expected between cousins.
    • It was uncousinly of him to spread that rumor about his own relative.
    • Her uncousinly attitude surprised everyone at the holiday dinner.
    • Refusing to help with the family reunion felt very uncousinly.
Antonyms
adverb
  1. In a manner that is not like a cousin; without the affection or loyalty expected between cousins.
    • She spoke uncousinly, as if they were strangers instead of family.
    • He acted uncousinly by ignoring her at the wedding.
    • They treated each other uncousinly, never exchanging a kind word.