Believer in a philosophical idea and its main ground (7)
I believe the answer is:
animist
'believer in a philosophical idea' is the definition.
'animist' can be an answer for 'believer' (I have seen 'Pagan believer ' mean 'animist' so perhaps 'believer' could also mean 'animist'). I am not sure about the 'in a philosophical idea' bit.
'its main ground' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'its'+'main'='itsmain'
'itsmain' with letters rearranged gives 'ANIMIST'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for animist that I've seen before include "Pagan believer" , "primitive worshipper?" , "One believing creatures and objects have souls" , "Witchdoctor maybe" , "One who sees life everywhere" .)