Crossword Genius

The head cleaner (7)

Ross

I believe the answer is:

shampoo

I'm a little stuck... Click here to teach me more about this clue!

This clue might be a double definition.

'the head' is the first definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'cleaner' is the second definition.
(shampoo cleans hair)

Can you help me to learn more?

(Other definitions for shampoo that I've seen before include "My partner may be set" , "Liquid that goes to your head?" , "Washer for locks" , "hair treatment" , "Hair-cleaning product" .)

I've seen this clue in The Globe and Mail.
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