They share an item in a geometry set (8)
I believe the answer is:
dividers
'item in a geometry set' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'they share an' is the wordplay.
I cannot quite see how this works, but
'share' could be 'divi' (short for dividend) and 'divi' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for dividers that I've seen before include "What may be found in geometry class" , "V-shaped measuring device" , "rulers?" , "Navigational or geometric instrument" , "Type of compass used for measuring distance" .)