headland vs promontory

headland and promontory both are nouns.

Word	Noun	Adjective	Verb	Adverb
headland	Yes	No	No	No
promontory	Yes	No	No	No

As nouns, headland and promontory are synonyms defined as:

headland and promontory: a natural elevation (especially a rocky one that juts out into the sea)

Other synonyms of headland include foreland, head.

headland (noun)	promontory (noun)
a natural elevation (especially a rocky one that juts out into the sea)	a natural elevation (especially a rocky one that juts out into the sea)