Grinder perhaps also extremely tough (5)
I believe the answer is:
tooth
'grinder perhaps' is the definition.
(I know that molar is a type of tooth)
'also extremely tough' is the wordplay.
'also' becomes 'too' (synonyms).
'extremely' suggests removing the centre (only the extremes of the word are used).
'tough' with its middle taken out is 'th'.
'too'+'th'='TOOTH'
(Other definitions for tooth that I've seen before include "Chopper" , "Gearwheel cog" , "Biter" , "1 across" , "Projection on comb, saw or wheel" .)