Trying a sour rum (7)
I believe the answer is:
onerous
'trying' is the definition.
(I've seen this before)
'a sour rum' is the wordplay.
'a' becomes 'one'.
'rum' indicates anagramming the letters (rum can mean strange or unusual).
'sour' is an anagram of 'rous'.
'one'+'rous'='ONEROUS'
(Other definitions for onerous that I've seen before include "Challenging" , "Toilsome" , "Effortful" , "Burdensome, taxing" , "Burdensome, oppressive" .)