Not looked after (8)
'not looked after' is the definition.
(I've seen this before)
'not looked after' is the wordplay.
'not' becomes 'un' (I've seen this in other clues).
'looked after' becomes 'tended' (tending is a kind of looking after).
'un'+'tended'='UNTENDED'
(Other definitions for untended that I've seen before include "Neglected" , "Not properly cared for" , "Left without attention or minder" , "Not looked after" .)
(Other definitions for neglected that I've seen before include "Ignored or failed to do" , "Failed to do or to attend to" , "Not cared for" , "Overgrown" , "Disregarded or failed to do something" .)