Such a failure could take Tom aback (3)
I believe the answer is:
mot
'such a failure could take' is the definition.
I can't judge whether this defines the answer.
'tom aback' is the wordplay.
'aback' says the letters should be written in reverse.
'tom' backwards is 'MOT'.
Can you help me to learn more?
(Other definitions for mot that I've seen before include "Clever remark" , "Wisecrack (for older cars!)" , "Word in France, bon perhaps" , "type of test" , "A French word, may be bon" .)