Reliable writer I rubbish? I have (13)
I believe the answer is:
authoritative
'reliable' is the definition.
(thesaurus)
'writer i rubbish? i have' is the wordplay.
'writer' becomes 'author' ('author' can be a synonym of 'writer'**).
'rubbish?' becomes 'tat' (I've seen this before).
'i have' becomes 'ive'.
'author'+'i'+'tat'+'ive'='AUTHORITATIVE'
(Other definitions for authoritative that I've seen before include "Reliably truthful and accurate" , "Definitive" , "Reliable, true" , "Reliable; commanding" , "Factual" .)