Plea from bookie's lady whose partner's late (7)
I believe the answer is:
dowager
This could be a double definition.
'plea from bookie's' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'lady whose partner's late' is the second definition.
(Other definitions for dowager that I've seen before include "Nobleman's widow" , "old lady" , "wealthy widow" , "Woman who holds title from dead husband" , "Wordage (anag.)" .)