IPA: /kəʊˈæksɪəli/
KK: /koʊˈæksɪli/
In a manner that shares a common central axis.
The two cylinders were aligned coaxially to ensure proper functioning.
Coaxially → It is formed from "co-" (meaning together) and "axial" (from Latin "axialis", meaning relating to an axis) and the suffix "-ly" (meaning in a manner). The word "coaxially" means in a manner that is together along the same axis.
Think of things being aligned 'together' ('co-') along an 'axis' — that's why coaxially means in a manner that is along the same axis.