Mentally sound (3,5)
'mentally sound' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sane that I've seen before include "Identical" , "Free from mental disorder" , "Mentally healthy" , "Mentally sound" , "Compos mentis" .)
(Other definitions for all there that I've seen before include "Fully compos mentis" , "sensible" , "fully alert" , "'''Is That ... Is?'' Peggy Lee song (3,5)'" , "mentally alert" .)