Crossword Genius

Optical instrument used to observe transparent material (8)

Ross

I believe the answer is:

spyglass

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

'optical instrument' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

'to observe transparent material' is the wordplay.
'to observe' becomes 'spy' (I am not sure about this - if you are sure you should believe this answer much more).
'transparent material' becomes 'glass' (I've seen this before).
'spy'+'glass'='SPYGLASS'

'used' acts as a link.

Can you help me to learn more?

(Other definitions for spyglass that I've seen before include "lookout's aid" , "he can see through it!" , "See-through article" , "Aid to pirate, perhaps" , "Small refracting telescope" .)

I've seen this clue in The Irish Times.
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