Poet mostly reserved about source of rhymes (6)

I believe the answer is:

brooke

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'poet' is the definition.
(I know that Brooke is a poet)

I cannot understand how the remainder of the clue works.

(Other definitions for brooke that I've seen before include "Rupert --, WW1 poet" , "Rupert --, English war poet" , "Versifying Rupert" , "Rupert __ , poet, d.1915" , "See 1" .)

I've seen this clue in The Times.

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