Once more put up half rain falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(thesaurus)
'once more put up half rain' is the wordplay.
'once more' becomes 'again' ('again' can be a synonym of 'once more').
'put up' says the letters should be written backwards.
'half' indicates taking half.
'again' reversed gives 'niaga'.
'rain' cut in half is 'ra'.
'niaga'+'ra'='NIAGARA'
(Other definitions for niagara that I've seen before include "Great waterfalls on Canadian-US border" , "Famous 12" , "It falls in North America" , "& 22 Down North American cascade" , "They fall in North America" .)