Parking licence is commonplace (9)
I believe the answer is:
platitude
'commonplace' is the definition.
(synonyms)
'parking licence' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'licence' becomes 'latitude' (I've seen this before).
'p'+'latitude'='PLATITUDE'
'is' is the link.
(Other definitions for platitude that I've seen before include "Trite remark made as if it were important." , "Commonplace remark uttered solemnly" , "Trite saying" , "Trite remark made as if meaningful" , "Commonplace remark uttered as if original" .)