Is no longer dated when done up (3)
I believe the answer is:
was
'is no longer' is the definition.
(I've seen this before)
'dated when done up' is the wordplay.
'dated' becomes 'saw' ('see' can be a synonym of 'date').
'when done up' says the letters should be written in reverse.
'saw' backwards is 'WAS'.
(Other definitions for was that I've seen before include "Lived" , "(He/she/it) existed" , "(I/he/she/it) existed" , "Did live" , "Used to be" .)