A songbird; a fungal infection, eg of the mouth (6)

I believe the answer is:

thrush

(Other definitions for thrush that I've seen before include "Speckled songbird or throat infection" , "Common British songbird" , "Speckle-breasted songbird" , "Throstle" , "Song bird" .)

I've seen this clue in The Sunday Times and The Times.

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