Protuberance reveals a cab (4)
I believe the answer is:
uber
'a cab' is the definition.
(Uber is a taxi app)
'protuberance reveals' is the wordplay.
'reveals' indicates a hidden word.
'UBER' can be found hidden inside 'protuberance'.
(Other definitions for uber that I've seen before include "Taxi company" , "App-based alternative to taxis" .)
I've seen this clue in the Sydney Morning Herald.
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