This writer is unhappy, forgetting bottom of hill's steep (5)

I believe the answer is:

imbue

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'steep' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for imbue that I've seen before include "Permeate, fill" , "Fill, with colour or feeling" , "Suffuse with colour" , "Permeate - inspire" , "Penetrate" .)

I've seen this clue in The Independent.

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