'antebrachial' originates from Latin, specifically the word 'antebrachium,' where 'ante-' meant 'before' and 'brachium' meant 'arm'.

'antebrachium' passed into Medieval/Neo-Latin as 'antebrachialis' (meaning 'of the forearm') and was borrowed into English as 'antebrachial'.

Initially it meant 'before the arm' (i.e., the part of the limb before the arm proper) and over time it came to mean specifically 'relating to the forearm', which is its modern anatomical sense.