Supplement found in road junction (7)
I believe the answer is:
adjunct
'supplement' is the definition.
(I've seen this in another clue)
'in road junction' is the wordplay.
'in' says the answer is hidden in the clue.
'ADJUNCT' can be found hidden inside 'road junction'.
'found' acts as a link.
(Other definitions for adjunct that I've seen before include "Something added, but not essential" , "Thing added" , "'Assistant, professor say (7)'" , "Something joined or added" , "Supplementary part" .)