From Longman Dictionary of Contemporary Englisharachnida‧rach‧nid /əˈræknɪd/ noun [countable] a small creature such as a spider, that has eight legs and a body with two parts
Examples from the Corpus
arachnid• Had they stewed up a supper of some giant arachnid for Tundrish?Origin arachnid (1700-1800) Greek arachne “spider” 