crossheading vs crosshead

crossheading and crosshead both are nouns.

Word	Noun	Adjective	Verb	Adverb
crossheading	Yes	No	No	No
crosshead	Yes	No	No	No

As nouns, crossheading and crosshead are synonyms defined as:

crossheading and crosshead: a heading of a subsection printed within the body of the text

crossheading (noun)	crosshead (noun)
a heading of a subsection printed within the body of the text	metal block that connects to a piston; it slides on parallel guides and moves a connecting rod back and forth
	a heading of a subsection printed within the body of the text