Hardworking threesome on river with us (11)
I believe the answer is:
industrious
'hardworking' is the definition.
(synonyms)
'threesome on river with us' is the wordplay.
'threesome' becomes 'trio' (both can mean a group of three).
'on' means one lot of letters go next to another.
'river' becomes 'indus' (Indian river).
'with' says to put letters next to each other.
'trio' put after 'indus' is 'industrio'.
'industrio'+'us'='INDUSTRIOUS'
(Other definitions for industrious that I've seen before include "Busy" , "Diligent, hard-working" , "Hard working" , "Toiling hard" .)