Old painter almost keeling over (4)
I believe the answer is:
aged
'old' is the definition.
(similar in meaning)
'painter almost keeling over' is the wordplay.
'painter' becomes 'Degas' (Edgar Degas, 1834-1917).
'almost' means to remove the last letter (most of the word but not all of it).
'keeling over' says the letters should be written backwards (in a down clue, words go up).
'degas' with its last letter removed is 'dega'.
'dega' in reverse letter order is 'AGED'.
(Other definitions for aged that I've seen before include "Antiquated" , "Old or ancient" , "not like a callow youth" , "not a modern copy" , "Grew older" .)