A two-way flier? (4)

I believe the answer is:

bird

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'flier?' is the definition.
(synonyms)

'a two-way' is the wordplay.
'a two' becomes 'bi' (I can't justify this - if you can you should believe this answer much more).
'way' becomes 'rd' (short for road).
'bi'+'rd'='BIRD'

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(Other definitions for bird that I've seen before include "Avian" , "Charlie "___" Parker - time inside" , "Egg-laying creature" , "Fowl" , "Nest builder?" .)

I've seen this clue in the Evening Standard.

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