Sarnie with no spread? Good thinking (9)
I believe the answer is:
reasoning
'thinking' is the definition.
(I know that thinking can be written as reasoning)
'sarnie with no spread? good' is the wordplay.
'with' says to put letters next to each other.
'spread?' indicates an anagram (I've seen 'spreading' mean this).
'good' becomes 'g' (abbreviation).
'sarnie' after 'no' is 'nosarnie'.
'nosarnie' anagrammed gives 'reasonin'.
'reasonin'+'g'='REASONING'
(Other definitions for reasoning that I've seen before include "sense?" , "Logical thought process" , "Thinking coherently and logically" , "Thinking that is coherent and logical" , "Train of thought" .)