Crossword Genius

Air filter (6)

Ross

I believe the answer is:

strain

This clue is a double definition.

'air' is the first definition.
(synonyms)

'filter' is the second definition.
(I know that filter can be written as strain)

(Other definitions for strain that I've seen before include "Injure (a muscle); distinct breed" , "Family - stress - air - force" , "Wrench; melody" , "Family; effort" , "Pour through a sieve" .)

I've seen this clue in The Telegraph and the Evening Standard.
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