Bleak possibility for an old sailor (5)

I believe the answer is:

blake

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'an old sailor' is the definition.
The definition suggests a singular noun which matches the answer.

'bleak possibility' is the wordplay.
'bleak' can be anagrammed to 'BLAKE'.
But, I'm unsure how the anagram is indicated.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for blake that I've seen before include "William -, English poet, artist and visionary" , "William -, (Jerusalem)" , "English poet and artist, d. 1827" , "Songs of Innocence poet" , "Exposed (to the air)" .)

I've seen this clue in the Evening Standard.

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