Not to mention the outlandish bit (3)
I believe the answer is:
and
'not to mention' is the definition.
(I've seen this in another clue)
'outlandish bit' is the wordplay.
'bit' says the answer is hidden in the clue.
'AND' can be found hidden inside 'outlandish'.
'the' acts as a link.
(Other definitions for and that I've seen before include "It's used to connect words, clauses or sentences" , "moreover" , "Together with" , "Word to connect" , "Most-used conjunction in English" .)