Hashira 柱 : A generic term for any type of pillar, column, post, pier and strut; the basic members of Japanese timber architecture.

ki 木 : tree or wood and, by extension building timber
main, chief, or master 主  

 

Tying to a vertical pillar, usually the main pillars that keep the traditional Japanese building erect.

This term has become synonymous with suspending from a vertical pole; vertical pole suspension (柱吊り)

 

See also: Floating Bamboo