noun
four pillars supporting the sumo ring roof
Historical sumo term; refers to the four posts that once supported the roof over the dohyō. No longer used in modern sumo, but still encountered in historical contexts.
昔の相撲では、四本柱が土俵の屋根を支えていた。
In old sumo, the four pillars supported the roof over the ring.
Compound of 四 (four), 本 (counter for long objects), and 柱 (pillar). The reading しほんばしら follows standard rendaku voicing on 柱.