Cautious line taken by US general (5)
I believe the answer is:
leery
'cautious' is the definition.
(thesaurus)
'line taken by us general' is the wordplay.
'line' becomes 'ry' (abbreviation for railway).
'taken by' means one lot of letters go next to another.
'us general' becomes 'lee'.
'ry' put after 'lee' is 'LEERY'.
(Other definitions for leery that I've seen before include "Sly, cunning" , "Cunning - wary" , "Knowing" , "Suspiciously cautious" , "In slang, wary or suspicious - reely!" .)