Nabokov's longest novel
I believe the answer is:
ada
'nabokov's longest novel' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ada that I've seen before include "Woman" , "Programming language" , "Computer lang.; f. name" , "Novel by Vladimir Nabokov" , "Palindromic girl's name" .)