Small matter of spy changing clue (8)
I believe the answer is:
molecule
'small matter' is the definition.
'molecule' can be an answer for 'matter' (thesaurus). I am not certain of the 'small' bit.
'spy changing clue' is the wordplay.
'spy' becomes 'mole' (I've seen this before).
'changing' indicates anagramming the letters.
'clue' is an anagram of 'cule'.
'mole'+'cule'='MOLECULE'
'of' is the link.
Can you help me to learn more?
(Other definitions for molecule that I've seen before include "Smallest particle of a substance" , "Smallest independently existing thing" , "Group of atoms bonded together" , "Tiny unit consisting of a group of atoms" , "Tiny particle" .)