Circles that woman in gym on board ship (7)

I believe the answer is:

spheres

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

'circles' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'woman in gym on board ship' is the wordplay.
'woman' becomes 'her' (her refers to a woman).
'in' indicates putting letters inside.
'gym' becomes 'pe' (short for Physical Education).
'on board' is an insertion indicator (inserted letters are taken on board).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'her' going inside 'pe' is 'phere'.
'phere' inserted within 'ss' is 'SPHERES'.

'that' acts as a link.

Can you help me to learn more?

(Other definitions for spheres that I've seen before include "Areas" , "balls" , "Globes" .)

I've seen this clue in The Mirror.

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