Wood that’s amazing outside, poor inside? (6)
I believe the answer is:
willow
'wood' is the definition.
(willow is a type of tree)
'amazing outside poor inside?' is the wordplay.
'amazing outside' becomes 'wow' (I am not sure about this - if you are sure you should believe this answer much more).
'poor' becomes 'ill' (I've seen this before).
'inside?' means one lot of letters goes inside another.
'wow' going around 'ill' is 'WILLOW'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for willow that I've seen before include "One [TYPE OF TREE]" , "Fast-growing tree" , "Quick-growing tree with flexible branches" , "It produces osiers" , "Common riverside tree" .)