___ Lovelace, Byron's daughter (3)
I believe the answer is:
ada
I believe this is a double definition.
'lovelace' is the first definition.
(computing pioneer Ada Lovelace)
'byron's daughter' is the second definition.
(I've seen this in another clue)
(Other definitions for ada that I've seen before include "Girl's name, one letter short of a man's name" , "Palindromic girl's name" , "Computer lang.; f. name" , "Woman" , "-- Lovelace, pioneer in computing" .)