frequency vs incidence

frequency and incidence both are nouns.

Word	Noun	Adjective	Verb	Adverb
frequency	Yes	No	No	No
incidence	Yes	No	No	No

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

frequency: the ratio of the number of observations in a statistical category to the total number of observations
incidence: the relative frequency of occurrence of something

Other hyponyms of frequency include relative incidence.

frequency (noun)	incidence (noun)
the number of observations in a given statistical category	the striking of a light beam on a surface
the ratio of the number of observations in a statistical category to the total number of observations	the relative frequency of occurrence of something
the number of occurrences within a given time period