"The Internet's first and only Malay-English dictionary" by D. K. Bhanot
Cornish is a P-gaelic language closely related to Welsh and Breton (as opposed to the Q-gaelic languages, Irish and its regional dialects Scots Gaelic and Manx). I was taught that Cornish went extinct when its last monoglot speaker, Dolly Pentreath, died in 1777. More recently people have begun to claim otherwise, and say that bilinguals with native knowledge of Cornish could still be found up until the late nineteenth century, by which time a revival had begun. This link is to a download page, not an online dictionary.
Most Gothic dictionaries are in German. This is because of the preponderance of German scholarship in the development of Indo-European philology. This English-Gothic dictionary has just over 950 "basic" words, which may not seem like a lot. But there is not much Gothic extant. This link is to a download page, and academia.eu will demand that you open an account.
A digitized version of Liddell & Scott (1940), a very Victorian dictionary, but still the standard in the English-speaking world. Configurable, so the Greek is transliterated or not as you prefer. From Tufts University. The website has clickable references to citations that have translations, most helpful to those of us with small Latin and less Greek.
From Mamta's Kitchen. Covers ingredients, methods of preparation and dishes of North Indian cuisine.
A link page to a large number of specialized vocabularies in Irish (librarianship, computing, parliamentary reporting, etc). The link page itself is in Irish only (for which Google Translate offers a surprisingly good translation — but don't click the links in the translated page because it will try to translate them too!). It may help to know that Béarla - Gaeilge means 'English - Irish' and foclóir means 'dictionary'.
A digitized version of Lewis & Short (1899), the standard Latin dictionary in the English-speaking world until 1982, when it was supplanted by the Oxford Latin Dictionary. From Tufts University. The site also has a morphology tool that will find a headword given an inflected form, very useful for those with small Latin and less Greek.
A free scanned and digitized edition of Bosworth & Toller, the 1898 classic that has yet to be supplanted, though scholars at the University of Toronto have got as far as L with a modern dictionary, that is also available online, and to which you get 20 free accesses per year if you sign up for an account.
A scanned edition of A Concise Dictionary of Old Icelandic (1910, 551 pp), by Geir T. Zoëga.
English-Old Norse dictionary compiled by Ross G. Arthur. A brief and very straightforward glossary in PDF format. Searchable, so you can use it as an Old Norse-English dictionary. Exemplary typography.
This dictionary contains all of the words from the glossary of Herbert Penzl's A grammar of Pashto: A descriptive study of the dialect of Kandahar, Afghanistan (Washington, DC: American Council of Learned Societies, 1955), pp. 154-165.