Mother that can't be fooled (6)
I believe the answer is:
nature
'mother that can't be fooled' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nature that I've seen before include "sort of reserve" , "Disposition, temperament" , "variety" , "Innate quality" , "The world with all its features found in tea-urn" .)