Crossword Genius

Out loud, I refer to what the Observer must use (8)

Ross

I believe the answer is:

eyesight

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

'what the observer must use' is the definition.
I can't judge whether this defines the answer.

'out loud i refer' is the wordplay.
'out loud' indicates a 'sounds like' (homophone) clue.
'refer' becomes 'sight' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i' is a homophone of 'eye'.
'eye'+'sight'='EYESIGHT'

'to' acts as a link.

Can you help me to learn more?

(Other definitions for eyesight that I've seen before include "quality of viewing" , "Purpose of certain organs" , "Power of vision" , "Faculty of vision" , "Visual faculty" .)

I've seen this clue in The Guardian.
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