After first suspicion, bestow in abundance and is painstakingly submissive (7)
I believe the answer is:
slavish
'submissive' is the definition.
(I know that submissive can be written as slavish)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for slavish that I've seen before include "Humble" , "Unoriginal" , "Blindly imitative" , "Menial" , "Submissive, servile" .)