13-Letter Words Matching ________I_O__

There are 21 13-letter words that match ________I_O__. 6 are common words, such as CARTILAGINOUS and MULTITUDINOUS. A rarer one is THERMOPHILOUS. In this set, N is the most frequent open letter (19 words). 5 words contain a doubled letter.

Full list 21

cartilaginousmultitudinousplatitudinousprimogenitorspusillanimousserendipitousanthraquinonecartilaginoidcolumelliformentomophilouspantechniconsphylloquinoneferrosiliconsnonleguminousplastoquinoneplenitudinousrectitudinousstereopticonssubbituminoussubinhibitorythermophilous

About this list

Words
21 (6 common words)
Common example
cartilaginous
Rare example
thermophilous
Doubled letters
5
Ending in S
15
Most frequent letter
N (19)

Questions

How many 13-letter words matching ________i_o__ are there?

21. 6 of them are common words.

What is a common example?

CARTILAGINOUS is among the common words in this set.