Something hard to eat outside? (5)
I believe the answer is:
crust
'outside?' is the definition.
(thesaurus)
'something hard to eat' is the wordplay.
'something hard' becomes 'c' (I am not sure about this - if you are sure you should believe this answer much more).
'to eat' becomes 'rust' ('rust' can be a synonym of 'eat').
'c'+'rust'='CRUST'
Can you help me to learn more?
(Other definitions for crust that I've seen before include "Hard outer coating" , "Outer part of loaf" , "Hard knowledge" , "Tough part of twenty two down" , "Hardened layer; pie top" .)