speaker vs bullhorn

speaker and bullhorn both are nouns.

Word	Noun	Adjective	Verb	Adverb
speaker	Yes	No	No	No
bullhorn	Yes	No	No	No

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

speaker: electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
bullhorn: a portable loudspeaker with built-in microphone and amplifier

speaker (noun)	bullhorn (noun)
electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance	a portable loudspeaker with built-in microphone and amplifier
someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)