horizontal merger vs merger

horizontal merger and merger both are nouns.

Word	Noun	Adjective	Verb	Adverb
horizontal merger	Yes	No	No	No
merger	Yes	No	No	No

As nouns, merger is a hypernym of horizontal merger; that is, merger is a word with a broader meaning than horizontal merger:

horizontal merger: a merger usually between two companies in the same business sector.
merger: the combination of two or more commercial companies

Other hypernyms of horizontal merger include amalgamation, uniting.

horizontal merger (noun)	merger (noun)
a merger usually between two companies in the same business sector.	the combination of two or more commercial companies
	an occurrence that involves the production of a union