Survey old people crossing a main road (11)
I believe the answer is:
examination
'survey' is the definition.
(thesaurus)
'old people crossing a main road' is the wordplay.
'old' becomes 'ex'.
'people' becomes 'nation'.
'crossing' means one lot of letters goes inside another.
'main road' becomes 'mi'.
'ex'+'nation'='exnation'
'a'+'mi'='ami'
'exnation' enclosing 'ami' is 'EXAMINATION'.
(Other definitions for examination that I've seen before include "Test of proficiency" , "School test" , "Detailed inspection" , "Formal test" , "Test of knowledge" .)