Crossword Genius

What Humphrey hung in the loo? (6)

Ross

I believe the answer is:

bogart

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'loo?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for bogart that I've seen before include "See 12" , "Humphrey --, US film actor" , "American actor" , "Rob gat from the old film star" , "Lauren Bacall's first actor husband, d. 1957" .)

I've seen this clue in The Guardian.
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