Pair of upbeat women (3)
I believe the answer is:
two
'pair' is the definition.
(a pair means two of something)
'of upbeat women' is the wordplay.
'of' indicates the answer is hidden within the clue.
'TWO' is hidden in the letters of 'upbeat women'.
(Other definitions for two that I've seen before include "Cat's coat" , "Couple, brace" , "not very many" , "Prime number" , "Number of faces of the god Janus" .)