Enough snowflakes to make flying dangerous? (4)

I believe the answer is:

flak

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'enough' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'snowflakes to make flying dangerous?' is the wordplay.
'FLAK' is hidden in amongst the letters.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for flak that I've seen before include "Brickbats" , "Ground-to-air attack: verbal abuse" , "Shooting" , "Anti-aircraft fire - strong criticism" , "Bad press" .)

I've seen this clue in the Evening Standard.

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