The following dictionaries and lexicons are available either in print or online.
Open-access: A Latin Dictionary (or Harpers' Latin Dictionary, often referred to as Lewis and Short or L&S) is a popular English-language lexicographical work of the Latin language, published by Harper and Brothers of New York in 1879 and printed simultaneously in the United Kingdom by Oxford University Press.
Open-access: Logeion is an open-access database of Latin and Ancient Greek dictionaries. Developed in 2011, it is hosted by the University of Chicago. Apart from simultaneous search capabilities across different dictionaries and reference works, Logeion offers access to frequency and collocation data from the Perseus Project.
Print, 2nd ed, 2 vols. (Oxford, 2011): The world's most authoritative dictionary of Classical Latin, the monumental, two-volume Oxford Latin Dictionary offers unsurpassed coverage of the language of Rome from its beginnings until AD 200. As well as 40,000 headwords and 100,000 senses, the Dictionary includes a vast collection of illustrative quotations taken from the canon of Classical literature, arranged for the first time conveniently under each sense and sub-sense.
Login required: The Thesaurus Linguae Latinae (TLL) is the most authoritative dictionary of ancient Latin. It is the only lexicon to cover all surviving Latin texts from the earliest times down to AD 600. Therefore it not only takes account of classical Latin but also treats in detail the special features of the language of late antiquity and Christian texts. As well as literary works, it examines medical and legal manuals, inscriptions, graffiti and many other types of text. There is also an open-access version made of the previous published volumes.
Print, 17 vols.; edited by R. E. Latham (Oxford, 1975-2013): The Dictionary of Medieval Latin from British Sources (DMLBS) is a British Academy research project at the University of Oxford. Based entirely on original research, the DMLBS is the most comprehensive dictionary of Medieval Latin to have been produced and the first ever to focus on British Medieval Latin. Note that while the dictionary is available online through Logeion, it is only searchable there by headwords.
Print, 2nd ed.; edited by René Hoven (Brill, 2006): This dictionary records the vocabulary of over 230 Latin prose authors from different regional backgrounds who wrote between c. 1300 and c. 1600, and gives translations in French and English in approximately 11,000 entries. A highly practical lexicon, it provides researchers, teaching staff and students in the field of Early Modern Studies with concise, essential information.
Print; by Michiel de Vaan (Brill, 2011): This new etymological dictionary covers the entire Latin lexicon of Indo-European origin. It consists of nearly 1900 entries, which altogether discuss about 8000 Latin lemmata. All words attested before Cicero are included, together with their first date of attestation in Latin. The dictionary also includes all the inherited words found in the other ancient Italic languages, such as Oscan, Umbrian and South Picene; thus, it also serves as an etymological dictionary of Italic.
Print, 2nd ed.; by J. F. Niermeyer (Brill, 2002): The Mediae Latinitatis Lexicon Minus is a highly practical lexicon, providing researchers, teaching staff and students in the field of medieval history with concise, essential information. It provides French, English and German translations for every entry of a Medieval Latin concept.
Open-access: Wiktionary is a multilingual, web-based project to create a free content dictionary of terms (including words, phrases, proverbs, etc.) in all natural languages, including Latin. These entries may contain definitions, pronunciation guides, inflections, usage examples, and related terms, among other features.