Ex-Viennese? What are the odds of that? (5)
I believe the answer is:
evens
'ex-viennese? what are the odds of that?' is the definition.
I can't judge whether this defines the answer.
'ex-viennese? what are the odds' is the wordplay.
'what are the odds' means one should take alternating letters (only the odd-numbered letters are used).
'ex'+'viennese'='exviennese'
The alternating letters of 'exviennese' are 'EVENS'.
(Other definitions for evens that I've seen before include "Makes equal" , "Levels - odds" , "Half a chance" , "decreases" , "Balanced odds" .)