tonic vs atonic

tonic is a noun but atonic is not a noun.

Word	Noun	Adjective	Verb	Adverb
tonic	Yes	Yes	No	No
atonic	No	Yes	No	No

tonic (noun)	atonic (noun)
a medicine that strengthens and invigorates
(music) the first note of a diatonic scale
a sweet drink containing carbonated water and flavoring
lime- or lemon-flavored carbonated water containing quinine

tonic (adjective)	atonic (adjective)
(used of syllables) bearing the principle stress, usually accompanied by a change in pitch	(used of syllables) carrying no stress
employing variations in pitch to distinguish meanings of otherwise similar words	characterized by a lack of tonus
of or relating to or producing normal tone or tonus in muscles or tissue
imparting vitality and energy
relating to or being the keynote of a major or minor scale