Gadget with bidirectional functions, I see! (6)
I believe the answer is:
doodah
'gadget' is the definition.
'with bidirectional functions i see' is the wordplay.
'with' is a charade indicator (letters next to each other).
'bidirectional functions' becomes 'do od' (a 'do' is a function/party; in both directions).
'i see' becomes 'ah' (exclamation used to indicate understanding).
'dood' put next to 'ah' is 'DOODAH'.
(Other definitions for doodah that I've seen before include "Whatchamacallit, thingamajig" , "Whatsitsname" , "one can't name" , "Thingamy" , "Thingummy" .)