Pronunciation: (rā'kis),[key] —n., —pl.ra•chis•es, rach•i•desPronunciation: (rak'i-dēz", rā'ki-).[key] 1. Bot. a. the axis of an inflorescence when somewhat elongated, as in a raceme.
b. (in a pinnately compound leaf or frond) the prolongation of the petiole along which the leaflets are disposed.
c. any of various axial structures.
2. Ornith.the part of the shaft of a feather bearing the web. See illus. under feather. 3. Anat.See spinal column.Also,rhachis.