Nails, say, hammered for research (8)
I believe the answer is:
analysis
'research' is the definition.
(thesaurus)
'nails say hammered' is the wordplay.
'hammered' indicates an anagram (slang term for drunk).
'nails'+'say'='nailssay'
'nailssay' with letters rearranged gives 'ANALYSIS'.
'for' is the link.
(Other definitions for analysis that I've seen before include "See 3" , "Investigation of the component parts which make up the whole" , "Examination of structure of problem" , "Dissection and examination" , "Detailed breakdown" .)