15-Letter Words Matching ____S_R________

There are 18 15-letter words that match ____S_R________. 8 are common words, such as BACKSCRATCHINGS and CLAUSTROPHOBIAS. A rarer one is UNDESIRABLENESS. In this set, I is the most frequent open letter (17 words). 7 words contain a doubled letter.

Full list 18

backscratchingsclaustrophobiasillustriousnessindustrializingindustriousnesspedestrianizingpressurizationsredistributionsbioastronauticsjurisprudentialsinistrodextraltranscriptionalunassertivenessindustrialisingmagistraticallynonastronomicalpleasurablenessundesirableness

About this list

Words
18 (8 common words)
Common example
backscratchings
Rare example
undesirableness
Doubled letters
7
Ending in S
10
Most frequent letter
I (17)

Questions

How many 15-letter words matching ____s_r________ are there?

18. 8 of them are common words.

What is a common example?

BACKSCRATCHINGS is among the common words in this set.