Sufficient backing for small cross-section (6)
I believe the answer is:
sample
'section' is the definition.
(thesaurus)
'sufficient backing for small' is the wordplay.
'sufficient' becomes 'ample' (both can mean enough).
'backing' is a charade indicator (letters next to each other).
'for small' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'ample' put after 's' is 'SAMPLE'.
'cross' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sample that I've seen before include "instance" , "Experience" , "Taste(r)" , "Taste; specimen" , "Take" .)