12-Letter Words Matching ________IR__

There are 13 12-letter words that match ________IR__. 6 are common words, such as BILLIONAIRES and DOCTRINAIRES. A rarer one is ZILLIONAIRES. 5 words contain a doubled letter.

Full list 13

billionairesdoctrinaireshummingbirdslegionnairesmillionairesmockingbirdsbutcherbirdscounterfiredcounterfiresoncornaviruspicornavirusthunderbirdszillionaires

About this list

Words
13 (6 common words)
Common example
billionaires
Rare example
zillionaires
Doubled letters
5
Ending in S
12

Questions

How many 12-letter words matching ________ir__ are there?

13. 6 of them are common words.

What is a common example?

BILLIONAIRES is among the common words in this set.