A show of heads? (4)

I believe the answer is:

hair

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'a show' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for hair that I've seen before include "Barber's speciality; musical" , "Human head covering" , "Famous hirsute musical with song ` `Aquarius' ' (4)" , "Fibre; small extent" , "Coiffure" .)

I've seen this clue in the Evening Standard.

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