15-Letter Words Matching A_____S________

There are 13 15-letter words that match A_____S________. 3 are common words, such as ADMINISTRATIONS and ATHEROSCLEROSES. A rarer one is ANTIOBSCENITIES. In this set, I is the most frequent open letter (12 words). 2 words contain a doubled letter.

Full list 13

administrationsatherosclerosesatherosclerosisagribusinessmanancylostomiasisankylostomiasisatheroscleroticagribusinessmenancylostomiasesankylostomiasesantifashionableantihistaminicsantiobscenities

About this list

Words
13 (3 common words)
Common example
administrations
Rare example
antiobscenities
Doubled letters
2
Ending in S
9
Most frequent letter
I (12)

Questions

How many 15-letter words matching a_____s________ are there?

13. 3 of them are common words.

What is a common example?

ADMINISTRATIONS is among the common words in this set.