Some help mistakenly gets rejected as stupid (6)
I believe the answer is:
simple
'stupid' is the definition.
(thesaurus)
'some help mistakenly gets rejected' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'rejected' says the letters should be written backwards.
'elpmis' is hidden within 'help mistakenly gets'.
'elpmis' written backwards gives 'SIMPLE'.
'as' is the link.
(Other definitions for simple that I've seen before include "The opposite of difficult or elaborate" , "Easy; herb" , "Impels (anag.)" , "Easily done/understood" , "Straightforward, not elaborate" .)