Be ill, perhaps, due to transgression (5)
I believe the answer is:
libel
'transgression' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'be ill perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'be'+'ill'='beill'
'beill' is an anagram of 'LIBEL'.
'due to' is the link.
Can you help me to learn more?
(Other definitions for libel that I've seen before include "Defamatory publication" , "Defame falsely" , "Written defamation" , "Published false statement that damages reputation" , "Write ill of" .)