'non-' originates from Latin, specifically the word 'non', where 'non' meant 'not'; 'arthropod' originates from Greek, specifically the words 'arthron' and 'pous' (or the combining form 'podos'), where 'arthron' meant 'joint' and 'pous/podos' meant 'foot'.

'arthropod' was coined in modern scientific usage (New Latin/19th century) from the Greek roots 'arthron' + 'pous/podos'; the compound 'non-arthropod' is formed by adding the negative prefix 'non-' to that scientific term to denote organisms that are not arthropods.

Initially, the Greek roots described 'jointed foot' anatomy; over time 'arthropod' became the technical term for animals of the phylum Arthropoda, and 'non-arthropod' simply came to mean 'not an arthropod'.