frequency vs oftenness

frequency and oftenness both are nouns.

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

As nouns, frequency and oftenness are synonyms defined as:

frequency and oftenness: the number of occurrences within a given time period

Other synonyms of frequency include frequence.

frequency (noun)	oftenness (noun)
the number of observations in a given statistical category	the number of occurrences within a given time period
the ratio of the number of observations in a statistical category to the total number of observations
the number of occurrences within a given time period