15-Letter Words Matching F_____O________

There are 12 15-letter words that match F_____O________. 4 are common words, such as FACETIOUSNESSES and FEROCIOUSNESSES. A rarer one is FUNCTIONALISTIC. In this set, I is the most frequent open letter (12 words). 8 words contain a doubled letter.

Full list 12

facetiousnessesferociousnessesfractiousnessesfrivolousnessesfideicommissaryforthcomingnessfugaciousnessesfunctionalitiesfeloniousnessesfibrinopeptidesfractionalizingfunctionalistic

About this list

Words
12 (4 common words)
Common example
facetiousnesses
Rare example
functionalistic
Doubled letters
8
Ending in S
9
Most frequent letter
I (12)

Questions

How many 15-letter words matching f_____o________ are there?

12. 4 of them are common words.

What is a common example?

FACETIOUSNESSES is among the common words in this set.