Unknown or not yet named
This is a rare modern usage, likely derived from the literal English phrase 'not named.' It is often found in historical records or medical contexts where a child's name was not recorded at birth, but it has occasionally been adopted as a unique, avant-garde personal name.
Less common today
Notnamed isn't in the latest US Top 1000. It last peaked at #1,234 in 2000.
US births per 5-year period, 1990βpresent (SSA data).