Only a few of one's friends are in shape (10)

I believe the answer is:

semicircle

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'only a few of one's friends' is the definition.
I can't judge whether this defines the answer.

'are in shape' is the wordplay.
'are in' becomes 'semi' (I can't explain this - if you can you should believe this answer much more).
'shape' becomes 'circle' (circle is a kind of shape).
'semi'+'circle'='SEMICIRCLE'

Can you help me to learn more?

(Other definitions for semicircle that I've seen before include "Half-moon shape" , "D, for example" , "D-shape" , "D shape, approximately" , "figure" .)

I've seen this clue in The Daily Express.

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