Shock finding uniform inside streetcar, American (6)
I believe the answer is:
trauma
'shock' is the definition.
(thesaurus)
'uniform inside streetcar american' is the wordplay.
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'inside' means one lot of letters goes inside another.
'streetcar' becomes 'tram' ('tram' can be a synonym of 'streetcar').
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'u' inserted inside 'tram' is 'traum'.
'traum'+'a'='TRAUMA'
'finding' is the link.
(Other definitions for trauma that I've seen before include "Emotional upset" , "Physical or mental shock" , "Lasting shock or disturbance" , "dreadful shock!" , "hurt" .)