13-Letter Words Matching _S__________Y

There are 18 13-letter words that match _S__________Y. 4 are common words, such as ASTONISHINGLY and ISOMETRICALLY. A rarer one is PSYCHOHISTORY. In this set, I is the most frequent open letter (16 words). 11 words contain a doubled letter.

Full list 18

astonishinglyisometricallypsychotherapypsychoticallyassignabilityassociativelyassociativityasthmaticallyostensibilitypsychobiologypsychosurgeryassortativelyasyndeticallyisochronouslyisosmoticallyisostaticallyoscillographypsychohistory

About this list

Words
18 (4 common words)
Common example
astonishingly
Rare example
psychohistory
Doubled letters
11
Ending in S
0
Most frequent letter
I (16)

Questions

How many 13-letter words matching _s__________y are there?

18. 4 of them are common words.

What is a common example?

ASTONISHINGLY is among the common words in this set.