half title vs bastard title

half title and bastard title both are nouns.

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

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

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

half title (noun)	bastard 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