Buoyant pound following Uruguayan peso to begin with (6)
I believe the answer is:
upbeat
'buoyant' is the definition.
(thesaurus)
'pound following uruguayan peso to begin with' is the wordplay.
'pound' becomes 'beat' (synonyms).
'following' says to put letters next to each other.
'to begin with' suggests taking the first letters.
The initial letters of 'uruguayan peso' is 'up'.
'beat' after 'up' is 'UPBEAT'.
(Other definitions for upbeat that I've seen before include "Optimistic, positive" , "Conductor's beginning" , "Optimistic - anacrusis" , "Cheerful and positive, as in music" , "signal from sergeant, say, at end of bar?" .)