Source of starch and projectile reversed? Too right (9)
I believe the answer is:
arrowroot
'source of starch' is the definition.
'arrowroot' can be an answer for 'starch' (arrowroot is a kind of starch). I am not certain of the 'source of' bit.
'projectile reversed? too right' is the wordplay.
'projectile' becomes 'arrow' (arrow is a kind of projectile).
'reversed?' says the letters should be written backwards.
'right' becomes 'r' (common abbreviation).
'too'+'r'='toor'
'toor' in reverse letter order is 'root'.
'arrow'+'root'='ARROWROOT'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for arrowroot that I've seen before include "that thickens" , "Medicinal plant" , "culinary powder" , "Carib foodstuff" , "Fine cooking powder" .)