15-Letter Words Matching ________E_R____

There are 17 15-letter words that match ________E_R____. 6 are common words, such as GEOENGINEERINGS and MICROMETEORITES. A rarer one is NONENGINEERINGS. In this set, I is the most frequent open letter (16 words). 6 words contain a doubled letter.

Full list 17

geoengineeringsmicrometeoritesmountaineeringsradiotelegraphsradiotelegraphytrigonometricalbioengineeringsconnoisseurshipgalvanometricalinterpenetratedinterpenetratesisoperimetricalphototelegraphyintracerebrallymicrometeoriticmicrometeoroidsnonengineerings

About this list

Words
17 (6 common words)
Common example
geoengineerings
Rare example
nonengineerings
Doubled letters
6
Ending in S
8
Most frequent letter
I (16)

Questions

How many 15-letter words matching ________e_r____ are there?

17. 6 of them are common words.

What is a common example?

GEOENGINEERINGS is among the common words in this set.