button vs horn button

button and horn button both are nouns.

Word	Noun	Adjective	Verb	Adverb
button	Yes	No	Yes	No
horn button	Yes	No	No	No

As nouns, horn button is a hyponym of button; that is, horn button is a word with a more specific, narrower meaning than button:

Other hyponyms of button include bell push, bell, buzzer, doorbell, mouse button, panic button, reset button.

button (noun)	horn button (noun)
a round fastener sewn to shirts and coats etc to fit through buttonholes	a button that you press to activate the horn of an automobile
an electrical switch operated by pressing
a device that when pressed will release part of a mechanism
any artifact that resembles a button
a specific area or icon in graphical user interface systems that is clicked or pressed in order to select a command or perform an action
a female sexual organ homologous to the penis
a round flat badge displaying information and suitable for pinning onto a garment
any of various plant parts that resemble buttons

button (verb)	horn button (verb)
fasten with buttons
provide with buttons