Be ill, perhaps, due to defamation (5)
I believe the answer is:
libel
'defamation' is the definition.
(libel is a kind of defamation)
'be ill perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'be'+'ill'='beill'
'beill' with letters rearranged gives 'LIBEL'.
'due to' is the link.
(Other definitions for libel that I've seen before include "Actionable words" , "Crime of publishing false statement that damages reputation" , "Calumnious writing" , "False and malicious publication to defame" , "Slanderous statements in print" .)