1) Namely 2) Namely, fancy 3) Phrase before a clarification 4) Phrase of elaboration 5) Specifically 6) That is 7) That is to say 8) Words of clarification 
prep. that is to say. Example: "the passengers in the vehicle, to wit: Arlene Jones, Betty Bumgartner and Sherry Younger."
Namely, that is to say, to know. Eg. The wonders of the world are , to wit: Opera house in Sydney, the Statue of Liberty .......