Current drop in unexpected income (8)

I believe the answer is:

windfall

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'income' is the definition.
(I know that windfall is a type of gain)

'current drop' is the wordplay.
'current' becomes 'wind' (wind is a type of current).
'drop' becomes 'fall' (synonyms).
'wind'+'fall'='WINDFALL'

'in unexpected' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for windfall that I've seen before include "An unexpected piece of luck - maybe an apple" , "Lucky acquisition" , "Piece of luck (but it might be bruised)" , "Godsend" , "Lucky bonus" .)

I've seen this clue in The Guardian and The Sun.

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