Perhaps buttonhole old Catholic concealed (6)

I believe the answer is:

orchid

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'perhaps buttonhole' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'old catholic concealed' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'catholic' becomes 'RC' (abbreviation for Roman Catholic).
'concealed' becomes 'hid' ('hide' can be a synonym of 'conceal').
'o'+'rc'+'hid'='ORCHID'

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(Other definitions for orchid that I've seen before include "Glamorous tropical flower" , "Lush and expensive tropical flower" , "Beautiful exotic flower" , "Exotic and much treasured flower" , "Exotic bloom" .)

I've seen this clue in The Guardian.

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