A fair on fire (6)

I believe the answer is:

alight

'on fire' is the definition.
(I know that on fire can be written as alight)

'a fair' is the wordplay.
'fair' becomes 'light' (as in fair hair).
'a'+'light'='ALIGHT'

(Other definitions for alight that I've seen before include "Descend, from a bus or train say" , "Touch down" , "Get down from, bus or plane" , "Get down from, say bus" , "Descend from vehicle" .)

I've seen this clue in The Times.

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