What's the good of us being at a loose end? (3)
I believe the answer is:
use
'what's the good' is the definition.
(in phrases like 'it's no good', 'any good?' etc)
'us being at a loose end?' is the wordplay.
'being at' means one lot of letters go next to another.
'end?' says to take the final letters (I've seen 'ending' mean this).
The last letter of 'loose' is 'e'.
'us'+'e'='USE'
'of' is the link.
(Other definitions for use that I've seen before include "Employ (something)" , "Employ; consume" , "Put to work" , "Employ, put into service" , "consume; exploit" .)