'median-axis' originates from Modern English as a compound of 'median' and 'axis', where 'median' originates from Latin 'medianus' (from 'medius') meaning 'in the middle', and 'axis' originates from Latin 'axis' meaning 'axle, axis'.

'median' came into English via Latin 'medianus' (from 'medius' meaning 'middle'); 'axis' is from Latin 'axis' (used in Late Latin/Medieval Latin) meaning 'axle' or 'axis'. The two elements were combined in Modern English to form the compound 'median axis' (often written with a hyphen as 'median-axis').

Initially the component words meant 'middle' ('median') and 'axle/axle-like rod' ('axis'); over time the compound came to be used to denote the central line or midline of a body or object (its present meaning).