15-Letter Words Matching S_________R____

There are 13 15-letter words that match S_________R____. 2 are common words, such as SEPTUAGENARIANS and STRAIGHTFORWARD. A rarer one is SUBPROLETARIATS. In this set, A is the most frequent open letter (12 words). 2 words contain a doubled letter.

Full list 13

septuagenariansstraightforwardsemicylindricalsemipornographysilviculturallysilviculturistssocioculturallysociohistoricalsolitudinariansstadtholderatesstadtholdershipstockbrokeragessubproletariats

About this list

Words
13 (2 common words)
Common example
septuagenarians
Rare example
subproletariats
Doubled letters
2
Ending in S
6
Most frequent letter
A (12)

Questions

How many 15-letter words matching s_________r____ are there?

13. 2 of them are common words.

What is a common example?

SEPTUAGENARIANS is among the common words in this set.