"Home page". The Historical Thesaurus of English. University of Glasgow. Retrieved 15 October 2019.
"Classification". The Historical Thesaurus of English. University of Glasgow. Retrieved 22 October 2014. An oversize, one-page listing of all categories in top three tiers is available for download here.
"Second Edition". The Historical Thesaurus of English. University of Glasgow. Retrieved 15 October 2019.