柱礎 is read as ちゅうそ (chuuso) and means plinth.
ちゅうそ
chuuso
ちゅうじょうへんあつき
distribution transformer
きそ
foundation
いしずえ
foundation stone
こくそ
pillar of state
ていそ
laying a cornerstone (foundation stone)
しんそ
base stone for the central pillar of a pagoda
うききそ
floating foundation
はしら
counter for buddhas, gods, nobles, etc.
はしらどけい
wall clock
はしらま
bay (space or distance between two pillars)
ちゅうたい
cylinder
はしらがき
introductory clause of a law, patent, etc.