13-Letter Words Matching __A______O___

There are 20 13-letter words that match __A______O___. 7 are common words, such as BOARDINGHOUSE and GRAVITATIONAL. A rarer one is TRANSPERSONAL. In this set, I is the most frequent open letter (16 words). 5 words contain a doubled letter.

Full list 20

boardinghousegravitationalpharmacopoeiareapportionedstaphylococcitransnationalweatherproofsarachnophobiaexaminationalpharmacologicquadrillionthtransactionaltranslationalblanketflowerblastomycosesblastomycosisfianchettoingquasiperiodictransfusionaltranspersonal

About this list

Words
20 (7 common words)
Common example
boardinghouse
Rare example
transpersonal
Doubled letters
5
Ending in S
3
Most frequent letter
I (16)

Questions

How many 13-letter words matching __a______o___ are there?

20. 7 of them are common words.

What is a common example?

BOARDINGHOUSE is among the common words in this set.