This is the 282nd most frequent Japanese word.
なん
"なん" means "what."
Here, 'なん' is used as part of 'なんで', which means 'why', indicating a reason or cause.
なんで遅れたの？
Why were you late?
In this sentence, 'なん' is used to ask 'what', signifying curiosity or inquiry about something.
それはなんですか？
What is that?
The word 'なん' in 'なんか' adds a nuance of 'somewhat' or 'kind of', used to express vagueness or uncertainty.