Spy enigmatic clue? Just a bit (8)
I believe the answer is:
molecule
'a bit' is the definition.
(thesaurus)
'spy enigmatic clue?' is the wordplay.
'spy' becomes 'mole' (mole is a kind of spy).
'enigmatic' indicates an anagram.
'clue' anagrammed gives 'cule'.
'mole'+'cule'='MOLECULE'
'just' acts as a link.
(Other definitions for molecule that I've seen before include "... One unit of alcohol perhaps" , "Smallest independently existing thing" , "Small group of atoms" , "Simplest unit of an element" , "Smallest unit of compound" .)