15-Letter Words Matching ____R_T________

There are 30 15-letter words that match ____R_T________. 7 are common words, such as CONFRATERNITIES and CONGRATULATIONS. A rarer one is SUPERSTIMULATES. In this set, I is the most frequent open letter (27 words). 5 words contain a doubled letter.

Full list 30

Common words

confraternitiescongratulationsinscrutablenesssuperstitiouslysuperstructuresunderstandinglyunderstatementsalgorithmicallychlorothiazidesinterstratifiedinterstratifieslogarithmically
confraternitiescongratulationsinscrutablenesssuperstitiouslysuperstructuresunderstandinglyunderstatementsalgorithmicallychlorothiazidesinterstratifiedinterstratifieslogarithmicallymajoritarianismsuperstructuralantirationalismantirationalistantirationalityconcretizationsexoerythrocyticgewurztraminersheterothallismshyperstimulatedhyperstimulatesinheritablenessprioritizationssclerotizationssecuritizationssemiretirementssuperstimulatedsuperstimulates

About this list

Words
30 (7 common words)
Common example
confraternities
Rare example
superstimulates
Doubled letters
5
Ending in S
17
Most frequent letter
I (27)

Questions

How many 15-letter words matching ____r_t________ are there?

30. 7 of them are common words.

What is a common example?

CONFRATERNITIES is among the common words in this set.