as yet vs than

as yet

adv
  • Up to the present; thus far. 

than

adv
  • At that time; then. 

conj
  • Used in comparisons, to introduce the basis of comparison. 

prep
  • introduces a comparison, and is associated with comparatives, and with words such as more, less, and fewer. Typically, it seeks to measure the force of an adjective or similar description between two predicates. 

How often have the words as yet and than occurred in a corpus of books? (source: Google Ngram Viewer )