A lot of additional material arrived back, offering little substance (9)
I believe the answer is:
emaciated
'a lot of additional material arrived back offering little' is the definition.
I can't judge whether this defines the answer.
'substance' is the wordplay.
I cannot really understand how this works, but
'substance' could be 'te' (Te is an example) and 'te' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for emaciated that I've seen before include "Abnormally thin and weak" , "skinny" , "Gaunt from disease or hunger" , "Very thin from starvation or illness" , "Thin from illness or hunger" .)