Backing up in simple honesty (4)
I believe the answer is:
help
'backing' is the definition.
(thesaurus)
'up in simple honesty' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'in' says the answer is hidden in the clue.
'pleh' is hidden within 'simple honesty'.
'pleh' reversed gives 'HELP'.
(Other definitions for help that I've seen before include "one by the Beatles" , "Be of benefit to" , "Contribute to the success of" , "Charity" , "Assist, aid" .)