'arachnidology' originates from New Latin/modern scientific coinage, ultimately from Greek 'aráchnē' meaning 'spider' combined with the suffix '-logy' from Greek 'logia' meaning 'study' or 'science of'.

'arachnidology' was formed by combining 'arachnid' (from New Latin 'Arachnida', itself from Greek 'aráchnē') with the English productive suffix '-ology' and entered English as a technical term in the modern period of zoological nomenclature.

Initially it meant 'the study of spiders/arachnids', and this meaning has been retained as its technical sense.