Here's why:
* "Neef" can mean "cousin" (male) or "nephew".
Therefore, the antonyms would be:
* For "cousin" (male): "Niece" (nies), "aunt" (tante), "uncle" (oom)
* For "nephew": "Niece" (nies)
Important note: Afrikaans distinguishes between male and female relatives. So, you'll need to specify the context to get the correct antonym.