15-Letter Words Matching _________T_T___

There are 21 15-letter words that match _________T_T___. 4 are common words, such as EXPERIMENTATION and INSTRUMENTATION. A rarer one is SACROSANCTITIES. In this set, I is the most frequent open letter (21 words). 3 words contain a doubled letter.

Full list 21

experimentationinstrumentationsupplementationtransplantationcounterpetitionovercompetetivereafforestationanticompetitivecomplementationinterdigitatinginterdigitationintervisitationnonexploitationnonexploitativenonquantitativeoverexpectationphotoexcitationpostdivestiturepreimplantationreaccreditationsacrosanctities

About this list

Words
21 (4 common words)
Common example
experimentation
Rare example
sacrosanctities
Doubled letters
3
Ending in S
1
Most frequent letter
I (21)

Questions

How many 15-letter words matching _________t_t___ are there?

21. 4 of them are common words.

What is a common example?

EXPERIMENTATION is among the common words in this set.