15-Letter Words Matching I____O_________

There are 21 15-letter words that match I____O_________. 2 are common words, such as IMMUNODEFICIENT and INSUBORDINATION. A rarer one is IRREFORMABILITY. In this set, N is the most frequent open letter (20 words). 17 words contain a doubled letter.

Full list 21

immunodeficientinsubordinationimmunochemistryimmunoglobulinsimmunologicallyinhomogeneitiesinopportunenessinsubordinatelyirrevocablenessimmunoassayableimmunoblottingsimmunocompetentimmunodiagnosesimmunodiagnosisimmunodiffusionimmunomodulatorimmunopathologyimmunotherapiesinteroperativesirreconcilablesirreformability

About this list

Words
21 (2 common words)
Common example
immunodeficient
Rare example
irreformability
Doubled letters
17
Ending in S
10
Most frequent letter
N (20)

Questions

How many 15-letter words matching i____o_________ are there?

21. 2 of them are common words.

What is a common example?

IMMUNODEFICIENT is among the common words in this set.