bastard title vs half title

bastard title and half title both are nouns.

Word	Noun	Adjective	Verb	Adverb
bastard title	Yes	No	No	No
half title	Yes	No	No	No

As nouns, bastard title and half title are synonyms defined as:

bastard title and half title: a first page of some books displaying only the title of the book

bastard title (noun)	half title (noun)
a first page of some books displaying only the title of the book	a first page of some books displaying only the title of the book