In turnover, hot and lush rhubarb (4)
I believe the answer is:
tosh
'rhubarb' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'in turnover hot and lush' is the wordplay.
'in turnover' says the letters should be written backwards (the word turns over or back).
'hot' becomes 'h' (abbreviation eg on taps).
'and' means one lot of letters go next to another.
'lush' becomes 'sot' (both can mean a drunk).
'h'+'sot'='hsot'
'hsot' written backwards gives 'TOSH'.
Can you help me to learn more?
(Other definitions for tosh that I've seen before include "Cobblers" , "[BLAH]" , "Nonsense (colloq.)" , "Scottish chum" , "mate!" .)