Bivouac on the American college grounds (6)
I believe the answer is:
campus
'college grounds' is the definition.
(I've seen this in another clue)
'bivouac on the american' is the wordplay.
'bivouac' becomes 'camp' (synonyms).
'on' means one lot of letters go next to another.
'the american' becomes 'us' (abbreviation for United States).
'camp'+'us'='CAMPUS'
(Other definitions for campus that I've seen before include "University premises" , "university territory" , "College estate" , "educational grounds" , "student quarters" .)