Sphere in sight (3)
I believe the answer is:
orb
This might be a double definition.
'sphere' is the first definition.
(orb is a kind of sphere)
'sight' is the second definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for orb that I've seen before include "Jewelled ornament" , "Sphere for a sovereign" , "Ceremonial globe carried by a monarch" , "The World" , "ball with cross" .)