Top desire to pinch lab salt (8)
I believe the answer is:
pinnacle
'top' is the definition.
(I know that top can be written as pinnacle)
'desire to pinch lab salt' is the wordplay.
'desire' becomes 'pine'.
'to pinch' is an insertion indicator.
'lab salt' becomes 'nacl' (I can't explain this - if you can you should believe this answer much more).
'pine' enclosing 'nacl' is 'PINNACLE'.
Can you help me to learn more?
(Other definitions for pinnacle that I've seen before include "The highest point, peak" , "Acme" , "The highest point, say of fame" , "Towering peak" , "tip-top" .)