running head vs running headline

running head and running headline both are nouns.

Word	Noun	Adjective	Verb	Adverb
running head	Yes	No	No	No
running headline	Yes	No	No	No

As nouns, running head and running headline are synonyms defined as:

running head and running headline: a heading printed at the top of every page (or every other page) of a book

running head (noun)	running headline (noun)
a heading printed at the top of every page (or every other page) of a book	a heading printed at the top of every page (or every other page) of a book