Pure nonsense, board trustworthy (9)
I believe the answer is:
reputable
'trustworthy' is the definition.
(thesaurus)
'pure nonsense board' is the wordplay.
'nonsense' is an anagram indicator.
'board' becomes 'table' ('table' can be a synonym of 'board').
'pure' is an anagram of 'repu'.
'repu'+'table'='REPUTABLE'
(Other definitions for reputable that I've seen before include "Regarded as fair" , "Respected" , "Well thought of" , "Trustworthy" , "Well-regarded" .)