Number of abstentions (3)
I believe the answer is:
ten
'number' is the definition.
(ten is a kind of whole number)
'of abstentions' is the wordplay.
'of' indicates a hidden word.
'TEN' can be found hidden inside 'abstentions'.
(Other definitions for ten that I've seen before include "time" , "Base of decimal system" , "Cardinal number" , "X-WORD" , "PM's address, Downing St" .)