Axis, Pivot
noun
The middle of the axis is where the axis is, of course, but it's also where the pivot is too.
ちゅうじく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
昨日、珊瑚虫の中軸骨格を夢に見た。
Last night I had a dream about a coral insect’s axial skeleton.