Reverse say, and stop a period of development (9)
I believe the answer is:
gestation
'a period of development' is the definition.
(I've seen this before)
'reverse say and stop' is the wordplay.
'reverse' is a reversal indicator.
'say' becomes 'eg'.
'and' is a charade indicator (letters next to each other).
'stop' becomes 'station' (I've seen this before**).
'eg' backwards is 'ge'.
'ge'+'station'='GESTATION'
(Other definitions for gestation that I've seen before include "Development (in womb)" , "Development over time" , "Period of development" , "Development of plan" , "as before being transported by coach" .)