Crossword Genius

A bit of Sol's rash? (7)

Ross

I believe the answer is:

sunspot

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'a bit' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'sol's rash?' is the wordplay.
'sol' becomes 'sun' (I've seen this in another clue).
'rash?' becomes 'spot' (I can't explain this - if you can you should give a lot more credence to this answer).
'sun'+'spot'='SUNSPOT'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for sunspot that I've seen before include "Dark cool patch on the surface of our nearest star" , "Solar surface blemish" , "Cool darker patch on our star" , "Solar cool patch" , "warm place" .)

I've seen this clue in The Irish News.
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