Strict vegetarian (5)
I believe the answer is:
vegan
'strict vegetarian' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for vegan that I've seen before include "Person refraining from using animal products in any way" , "One not eating animals" , "An extreme vegetarian" , "Avoiding animal products" , "one not using animals" .)