Why is the ninth month called September?
1590s, "act of putting in," from Late Latin insertionem (nominative insertio), noun of action from past participle stem of inserere (see insert). Meaning "that which is inserted" attested from 1620s.
insertion in·ser·tion (ĭn-sûr'shən)
The point or mode of attachment of a skeletal muscle to the bone or other body part that it moves.
The placing of a dental prosthesis in the mouth.