Wait patiently (3,5)
(Other definitions for sit tight that I've seen before include "Refuse to be diverted" , "Maintain one's seat" , "Don't move" , "Keep one's position" , "Wait and see!" .)
'wait patiently' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bide that I've seen before include "Dwell, of old" , "Remain (archaic)" , "Remain or stay (poetically)" , "Remain; await (time)" , "Stay (obs.)" .)