Is the word "what" a conjunction in "I know what you meant."

Yes, it's an introductory conjunction.

Anonymous

I ask it because when I remove it I get two sentences. "I know." and "You meant".

I know what you meant.

No, it's not a conjunction.

The underlined expression is a subordinate interrogative clause (embedded question).

The interrogative word "what" is fronted, but it actually functions as complement of the verb

AnonymousI ask it because when I remove it [what] I get two sentences. "I know." and "You meant".

I see, here, "what" as a fused relative, i.e., "I know the thing which you meant". In my opinion, it is questionable to see "what you meant" as an indirect question in "I know what you meant".