This is the 753rd most frequent Icelandic word.
hve
The Icelandic word "hve" means "how."
Here, 'hve' is used as an interrogative pronoun asking 'how' in the context of 'how many'.
Hve margar bækur hefurðu lesið?
How many books have you read?
In this sentence, 'hve' introduces a clause indicating 'how' in the context of 'how fast'.
Ég veit ekki hve hratt hann er.
I don't know how fast he is.
Here, 'hve' is utilized to express 'how' in an introspective or qualitative sense, referring to 'how much importance'.