Creature lawn firm fails regularly to rub out (6)
I believe the answer is:
animal
'creature' is the definition.
(I know that creature can be written as animal)
'lawn firm fails regularly to rub out' is the wordplay.
'regularly to rub out' means one should take alternating letters (letters erased at regular intervals).
'lawn'+'firm'+'fails'='lawnfirmfails'
The alternate letters of 'lawnfirmfails' are 'ANIMAL'.
(Other definitions for animal that I've seen before include "savage" , "Neither vegetable nor mineral" , "Beastly" , "See 26" , "Man or beast" .)