tonic accent vs emphasis

tonic accent and emphasis both are nouns.

Word	Noun	Adjective	Verb	Adverb
tonic accent	Yes	No	No	No
emphasis	Yes	No	No	No

As nouns, emphasis is a hypernym of tonic accent; that is, emphasis is a word with a broader meaning than tonic accent:

tonic accent: emphasis that results from pitch rather than loudness
emphasis: the relative prominence of a syllable or musical note (especially with regard to stress or pitch)

Other hypernyms of tonic accent include accent, stress.

tonic accent (noun)	emphasis (noun)
emphasis that results from pitch rather than loudness	intensity or forcefulness of expression
	the relative prominence of a syllable or musical note (especially with regard to stress or pitch)
	special and significant stress by means of position or repetition e.g.
	special importance or significance