Think deeply about (7)
'think deeply about' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ponder that I've seen before include "Reflect" , "Think carefully" , "Consider deeply" , "Muse" , "Give thought to" .)
(Other definitions for reflect that I've seen before include "Cogitate" , "Ponder; send back" , "Echo, mirror" , "Ponder or produce an image" , "Contemplate like mirror" .)