1
general::
1. Also, as well as. For example, They study their instruments and, in addition, theory and music history. 2. in addition to. Over and above, besides, as in In addition to a new muffler, the truck needs new brakes. [c. 1900]
American Heritage Idioms
2
general::
Phrase(s): in addition (to something)
additionally; further; moreover; as an additional thing or person. • In addition, I would like for you to sweep the kitchen floor. • I put the books away, and in addition to that, I cleaned up my desk.
McGrawhill's American Idioms And Phrasal Verbs