Crossword Genius

Bitter winter frost ends, sharp (5)

Ross

I believe the answer is:

alert

'sharp' is the definition.
('alert' can be a synonym of 'sharp')

'bitter winter frost ends' is the wordplay.
'bitter' becomes 'ale' ('ale' can be a synonym of 'bitter').
'ends' says to take the final letters.
The final letters of 'winter frost' are 'rt'.
'ale'+'rt'='ALERT'

(Other definitions for alert that I've seen before include "Watchful, quick-thinking" , "Wide-awake and watchful" , "Lively" , "Wide awake and watchful" , "On one's toes" .)

I've seen this clue in The Times.
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