ippon-jime, "to clap hands once to close (an event)".
After a cheerful party with a large number of local students, the organizer asked every one to stand in a circle and to do "一本締め". It is a new experience to many of those Japanese learners. A few asked me in a true interest, some worried whether or not it is a sort of ritual, and a few have already opened their electronic dictionaries. Certainly they found out the answer very soon.
On the way back to my accommodation, I saw another group of students to practice this one outdoor. It is a scene of student life in a spring night. However I was rather surprised to be ware that many dictionaries do not have an entry for this word.