teething vs ontogeny

teething and ontogeny both are nouns.

Word	Noun	Adjective	Verb	Adverb
teething	Yes	No	No	No
ontogeny	Yes	No	No	No

As nouns, ontogeny is a hypernym of teething; that is, ontogeny is a word with a broader meaning than teething:

teething: the eruption through the gums of baby teeth
ontogeny: (biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level

Other hypernyms of teething include development, growing, growth, maturation, ontogenesis.

teething (noun)	ontogeny (noun)
the eruption through the gums of baby teeth	(biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level