Snub lacking in substance (6)
I believe the answer is:
slight
'snub' is the definition.
(I know that snub can be written as slight)
'lacking in substance' is the wordplay.
I cannot really understand how this works, but
'substance' could be 'li' (Li is an example) and 'li' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for slight that I've seen before include "trivial" , "Deliberately discourteous act" , "A disrespectful reference - not great" , "Trifling - snub" , "Small in extent" .)