'antineutron' originates from English coinage combining the prefix 'anti-' (from Greek 'anti', ἀντί) meaning 'against, opposite' and 'neutron' (from Modern Latin/Greek 'neutron') meaning 'neutral particle'.

'antineutron' was formed in the mid-20th century following the discovery and naming of 'neutron' (early 20th century) and the subsequent use of the prefix 'anti-' to denote corresponding antiparticles; thus 'neutron' + 'anti-' yielded the modern term 'antineutron'.

Initially coined to denote the particle opposite to the neutron, its meaning has remained consistent as the designated antiparticle of the neutron.