Aid to viewing a singular spectacle? (7)

I believe the answer is:

monocle

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

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for monocle that I've seen before include "Reading glass for one eye only" , "Single eyeglass" , "optical device" , "lens" , "One-lens seeing apparatus" .)

I've seen this clue in the Evening Standard.

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