Beginning with the passe group (6)
I believe the answer is:
outset
'beginning' is the definition.
(I know that beginning can be written as outset)
'with the passe group' is the wordplay.
'with' means one lot of letters go next to another.
'the passe' becomes 'out' (I've seen this in another clue).
'group' becomes 'set' (both can mean a collection).
'out' next to 'set' is 'OUTSET'.
(Other definitions for outset that I've seen before include "origin" , "launch" , "Inception" , "Beginning, start" , "Starting point" .)