Crossword Genius

Said drunkenly one had a haircut (7)

Ross

I believe the answer is:

shingle

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'haircut' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for shingle that I've seen before include "Bob" , "Small beach pebbles" , "beach? Yes and no" , "Loose stones" , "A mass of seashore pebbles" .)

I've seen this clue in the Evening Standard.
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