Foggy — incomprehensible (6)

I believe the answer is:

opaque

This clue is a double definition.

'foggy' is the first definition.
(similar in meaning)

'incomprehensible' is the second definition.
(similar in meaning)

(Other definitions for opaque that I've seen before include "Impervious to light - hard to understand" , "Without lustre" , "Cloudy, non-transparent" , "Incomprehensible, impenetrable" , "Mysterious" .)

I've seen this clue in The Guardian.

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