Learn Icelandic: Vanþekkingin hræðir mig.

The root noun here is þekking, which means "knowledge". The prefix van- indicates a lack, deficiency, or opposite of something (similar to "under-", "mal-", or "un-" in English). So, vanþekking literally translates to a "lack of knowledge" or "ignorance".

Is the prefix van- used the same way as the negative prefix ó-?

Not exactly. While ó- usually implies a simple "not" or creates a direct opposite, van- specifically implies a deficiency, inadequacy, or something being done poorly. Therefore, vanþekking focuses on an inadequate amount of knowledge rather than just an abstract opposite.

Why does vanþekkingin end in -in?

Nouns ending in the suffix -ing (like þekking) are almost universally feminine in Icelandic. The -in suffix is the feminine singular definite article attached to the end, turning "ignorance" into "the ignorance".

Why do we use mig here instead of the dative mér?

The verb hræða (to scare or frighten) requires its direct object to be in the accusative case. Since the ignorance is doing the scaring, the person being scared is the object. The accusative form of "me" is mig.