Both arduous and difficult inside (4)
I believe the answer is:
hard
'difficult inside' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'both arduous' is the wordplay.
'HARD' is hidden in amongst the letters.
But, I am uncertain how this is indicated.
'and' is the link.
Can you help me to learn more?
(Other definitions for hard that I've seen before include "Firm; demanding; stern" , "Complicated" , "Difficult - firm" , "Firm, rigid, road leading to foreshore" , "Difficult; severe" .)