Sometimes lexicography is considered to be a part or a branch of lexicology, but properly speaking, only lexicologists who write dictionaries are lexicographers.

Some consider this a distinction of theory vs. practice.

An allied science to lexicology is lexicography, which also studies words, but primarily in relation with dictionaries – it is concerned with the inclusion of words in dictionaries and from that perspective with the whole lexicon

Not to be confused with lexicography.