Identify a lexical gap in English and explain why that gap might exist.

For example: There is no word in English for the parent of a half sibling that they don't share. This leads to people saying things like "My sister's dad. Not my dad, we have different fathers." which can lead to confusion. This gap might exist because English speakers have a limited view of family and people in this situation might avoid speaking about parents they don't share with half siblings because English speakers want to avoid the awkwardness.