That is to say (6)
(Other definitions for namely that I've seen before include "to wit" , "Old especially" , "Videlicet" , "Viz" , "That is to say, specifically" .)
'that is to say' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for videlicet that I've seen before include "that is to say" , "in other words" , "to wit" , "Viz. in full, namely" .)