libel vs defame

libel is a noun but defame is not a noun.

Word	Noun	Adjective	Verb	Adverb
libel	Yes	No	Yes	No
defame	No	No	Yes	No

As verbs, defame is a hypernym of libel; that is, defame is a word with a broader meaning than libel:

libel: print slanderous statements against
defame: charge falsely or with malicious intent; attack the good name and reputation of someone

Other hypernyms of libel include asperse, besmirch, calumniate, denigrate, slander, smear, smirch, sully.

libel (noun)	defame (noun)
a false and malicious publication printed for the purpose of defaming a living person
the written statement of a plaintiff explaining the cause of action (the defamation) and any relief he seeks

libel (verb)	defame (verb)
print slanderous statements against	charge falsely or with malicious intent; attack the good name and reputation of someone