This presentation of Old English vocabulary is conceptually arranged, and is therefore entitled A Thesaurus of Old English (TOE). The vocabulary of Anglo-Saxon England is presented within ordered categories.
Ideally, the reader should approach the materials of the TOE by subject rather than through the alphabetic index of the printed edition. Roget-owners have long been accustomed to begin with a word and, by trying a few locations listed in the index, find the vocabulary group wanted. Moreover, for inclusiveness they trade detailed information. Should a word's precise meaning be wanted, a dictionary is needed. Most conceptually-organized thesauri tend therefore to be used by native speakers of a language, who know the meanings of the words scanned. Less assured speakers may turn to those alphabetically-organized thesauri where they will find more help with meaning but far fewer words. In the TOE any small group of items listed together as sharing a component of meaning resembles the strings of words that make up the entries of an alphabetically-organized thesaurus, but they are embedded within an inclusive conceptual scheme. The provision of brief indications of meaning at all levels of this scheme looks back behind Roget, to the way in which Wilkins supplies notions and words, where word-senses follow on from ideas explained. Thus, this thesaurus incorporates information about word meaning and could be described as an inside-out dictionary, with meanings first and then words.
For the contents of the TOE dictionaries have indeed been turned inside out, a task initially undertaken to supply the editors of the Historical Thesaurus (HT) both with some idea of the range of Old English vocabulary not to be found in the Oxford English Dictionary (OED) and with a body of materials from which a pilot thesaurus could be made. The standard Old English dictionaries contain vocabulary for over five hundred years of the history of the language: little probably from the eighth century, much more from the ninth century, more again from the turn of the tenth century, and most from the eleventh and twelfth centuries. Because the OED generally omits those words that had dropped out of use by 1150, the TOE provides a complementary overview of the earliest vocabulary of English. The vocabulary is drawn essentially from pre-Norman England, the slips used in its compilation representing the work of generations of Anglo-Saxon scholarship. Within the wider context of the HT, it is useful that the TOE's contents trickle over into the twelfth century and sometimes beyond. With the completion of the HT, correspondences between the OED-derived word senses and the independently excerpted Old English were matched, and it was possible then both to accept all Old English slips matched up with OED-derived slips as validated and for the first time to assess the range of early English vocabulary altogether omitted from the OED.
Notes to the online third edition
We have taken the opportunity of the online publication of A Thesaurus of Old English to make a number of corrections and additions. These are mostly minor, concentrating on the spelling of head-words. A few words have also been added, removed or recategorised, but this type of revision has been kept to a minimum.
Without an agreed list of head-words for Old English, there is little hope of achieving uniformity of spelling. Some regularization was attempted in the final stages of editing the original A Thesaurus of Old English, and we have now tried to iron out a few of the more obvious remaining inconsistencies. For example, there is now one headword for stil(l)nes instead of five entries, and some mistaken length marks have been altered, with such stray forms as ādleg and gefāran now joining ādlēg and gefaran respectively in the Index volume. Occasionally unstressed vowels are harmonized, as with corþor, corþer and corþr, cildcradol and cildcradul, pearroc and pearruc, and wlenc(u) and wlenc(o), and more alternatives between forms with -i- and -y- have been brought together, for example cwildberendlic and cwyldberendlic, (ge)drinc and (ge)drync, gedrinca and gedrynca, firentācnian and fyrentācnian, forbrītan and forbrȳtan, gimmian and (ge)gymmian, þryng and geþring. Sometimes, however, the inconsistencies have been retained, as providing more information than would regularized forms (both -i- and -y- appear in the cyrice group), and this is particularly the case if flags are involved.
 Peter Mark Roget, Thesaurus of English Words and Phrases, London, 1853.
 Two useful introductions to the history of English dictionaries are: Tom McArthur, Worlds of Reference, Cambridge 1986; and Sidney I. Landau, Dictionaries: The Art and Craft of Lexicography, New York, 1984.
 John Wilkins, An Essay towards a Real Character and a Philosophical Language, London, 1668.
 The Oxford English Dictionary, ed. J. A. H. Murray and William Craigie, Oxford, 1933.
 Jane Roberts. ‘Towards an Old English Thesaurus’, Poetica, 9 (1978), 56-72.