'central-axis' is formed from the adjective 'central' and the noun 'axis'. 'central' ultimately comes from Latin 'centralis' (via Latin 'centrum' from Greek 'kentron'), where 'kentron' meant 'center'. 'axis' comes from Latin 'axis', meaning 'axle' or 'pivot'.

The element 'central' entered English from Late Latin/Old French forms derived from Latin 'centralis', itself from Latin 'centrum' (from Greek 'kentron'). 'Axis' was borrowed from Latin 'axis'. In Modern English these elements combined in technical, architectural, and scientific contexts to form 'central axis' (often hyphenated as 'central-axis' when used attributively).

Originally referring separately to 'center' and 'axle/pivot', the combined phrase came to mean the primary line around which parts are arranged or rotate; the sense has narrowed to denote a main center line or line of symmetry/rotation.