Stimulate flower, introducing uranium (5)
I believe the answer is:
rouse
'stimulate' is the definition.
(I've seen this before)
'flower introducing uranium' is the wordplay.
'flower' becomes 'rose' (I've seen this before).
'introducing' indicates putting letters inside (some letters introduced or inserted into others).
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'rose' placed around 'u' is 'ROUSE'.
(Other definitions for rouse that I've seen before include "Cause to become awake" , "Cause to wake up and come alert" , "Inspire" , "Provoke" , "Stir up; excite" .)