Crossword Genius

Wine or tot knocked back by trainee (8)

Ross

I believe the answer is:

muscadet

'wine' is the definition.
(Muscadet is an example)

'tot knocked back by trainee' is the wordplay.
'tot' becomes 'sum' ('sum' can be a synonym of 'tot').
'knocked back' shows that the letters should be reversed in order.
'by' says to put letters next to each other.
'trainee' becomes 'cadet' (cadet is a kind of trainee).
'sum' backwards is 'mus'.
'mus'+'cadet'='MUSCADET'

'or' acts as a link.

(Other definitions for muscadet that I've seen before include "drink" , "Dry white wine from the Loire valley" , "one of the Whites" , "Dry French white wine" , "White wine variety" .)

I've seen this clue in The Telegraph.
Want a hint initially instead of a full solution? Install my app