libeler vs maligner

libeler and maligner both are nouns.

Word	Noun	Adjective	Verb	Adverb
libeler	Yes	No	No	No
maligner	Yes	No	No	No

As nouns, libeler and maligner are synonyms defined as:

libeler and maligner: one who attacks the reputation of another by slander or libel

Other synonyms of libeler include backbiter, defamer, slanderer, traducer, vilifier.

libeler (noun)	maligner (noun)
one who attacks the reputation of another by slander or libel	one who attacks the reputation of another by slander or libel