15-Letter Words Matching I_________O____

There are 13 15-letter words that match I_________O____. 6 are common words, such as INCONSPICUOUSLY and INSTANTANEOUSLY. A rarer one is INTRAPERITONEAL. In this set, N is the most frequent open letter (12 words). 6 words contain a doubled letter.

Full list 13

inconspicuouslyinstantaneouslyinsurrectionistinterrogatoriesinterventionisminterventionistimprovisatorialinsurrectionaryinterrogatorilyimmunopathologyinefficaciouslyinternucleotideintraperitoneal

About this list

Words
13 (6 common words)
Common example
inconspicuously
Rare example
intraperitoneal
Doubled letters
6
Ending in S
1
Most frequent letter
N (12)

Questions

How many 15-letter words matching i_________o____ are there?

13. 6 of them are common words.

What is a common example?

INCONSPICUOUSLY is among the common words in this set.