Flower thoughtless Hindu god sent up (9)
I believe the answer is:
amaryllis
'flower' is the definition.
(I've seen this before)
'thoughtless hindu god sent up' is the wordplay.
'thoughtless' becomes 'silly' (silly can mean thoughtless or foolish).
'hindu god' becomes 'Rama' (Rama is an example).
'sent up' says the letters should be written backwards.
'silly'+'rama'='sillyrama'
'sillyrama' back-to-front is 'AMARYLLIS'.
(Other definitions for amaryllis that I've seen before include "Sly alarm I turn on for the flower" , "Showy bulbous plant" , "Plant with showy flowers - I rally Sam (anag)" , "Trumpet-flowered bulb" , "belladonna lily brought this about" .)