Note doughnut with new taste, possibly rhubarb (8)
I believe the answer is:
nonsense
'rhubarb' is the definition.
(I've seen this before)
'note doughnut with new taste possibly' is the wordplay.
'note' becomes 'n' (abbreviation).
'doughnut' becomes 'o' (letter resembling a doughnut).
'with' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'taste possibly' becomes 'sense' (taste is a kind of sense).
'n'+'o'+'n'+'sense'='NONSENSE'
(Other definitions for nonsense that I've seen before include "Codswallop, hooey" , "'Foolishness, silliness (8)'" , "Baloney" , "Boloney, tosh" , "hot air" .)