Add a dictionary to your Mac:
the steps and the gaps

The steps in the Dictionary app

Open Dictionary (it is in Applications, or press ⌘Space and type its name). In the menu bar choose Dictionary, then Settings. Apple's Dictionary guide says you can select and reorder sources there, such as Spanish or Korean dictionaries. Tick the ones you want. A source that is not yet on your Mac downloads when you tick it, and Apple says to wait for it to finish before you search.

Drag the rows to set the order. The sources you tick decide what Dictionary shows and what Look Up uses everywhere else on the Mac. Some sources have options of their own, such as how pronunciations are displayed or which language of Wikipedia is searched.

Which languages Apple offers

No single current list appears on Apple's help pages, so the list in Settings is the one to trust, and it can differ by macOS version and region. To read it on your own Mac, open Dictionary, Settings, and scroll the whole column.

For a reference point: on a Mac running macOS 26.5, the catalogue of Dictionary sources held 86 entries when it was read on 3 November 2026. They include Spanish and Spanish to English, French, German to English, Italian, Portuguese, Dutch, Russian, Greek, Turkish, Polish, Korean and Korean to English, Thai and Thai to English, Arabic to English, Hebrew and Hebrew to English, Hindi, Urdu to English, Vietnamese, Indonesian, several Chinese dictionaries (Simplified, Traditional, Cantonese, idioms) and a Chinese to Japanese one.

For Japanese there are two: Sanseido Super Daijirin, a Japanese dictionary, and the Sanseido Wisdom English-Japanese and Japanese-English dictionary. Neither Persian nor a medical dictionary appears in that catalogue.

Changing which dictionary answers first

Settings has no single dictionary language switch. What answers first is just the order of the ticked sources. To make a Spanish to English dictionary answer ahead of the English ones, tick it and drag it to the top of the list. To stop an English entry appearing at all, untick it. Wikipedia's language is a separate option on the Wikipedia source.

Adding a third-party dictionary file

Dictionaries from outside Apple come as a file ending in .dictionary. The guides found agree on the method: put the file in the ~/Library/Dictionaries folder, reopen Dictionary, and tick it in Settings. Make Tech Easier says the folder can be opened from Dictionary with File, then Open Dictionaries Folder, and that the app loads the file the next time it opens. The menu item is present in Dictionary on macOS 26.5. If the folder does not exist, you can create it inside your Library folder.

Two cautions. These guides are old, and the same article warns that many of the sites that hosted custom dictionaries are now defunct, so finding a trustworthy file is the hard part. And a file from an unknown site is a file from an unknown site: use sources you would trust with any other download. No third-party dictionary has been tested on the latest macOS for this page.

What to do for medical, Persian, Thai and the rest

Apple's dictionaries are general-purpose. They do not cover specialist fields such as medicine, and the catalogue above has no Persian entry. For a field, a third-party file is the traditional answer when you can find a good one. For clinical shorthand, a word list is not enough anyway, because the same abbreviation means different things in different notes. That is covered on the medical abbreviations page.

LeafyApp takes a different route. Press ⌥A, drag a box over the word in any app, and macOS text recognition reads that patch of screen. The answer is the meaning of the word in the sentence around it, written by an AI, so it is not limited to a dictionary's word list or to the languages Apple ships. That is useful for Thai, Arabic, Hebrew and Greek words, and for fields without a dictionary. It is an AI answer and it can be wrong, so check anything that matters. For a script macOS cannot read, the box has nothing to read in the first place.

Every word is saved with its sentence, source and date, and you can import a word list of your own.

If you want nothing sent anywhere

LeafyApp has a No-AI mode. With it on, lookups come from what is already on your Mac, your own saved entries and your Anki cards, and the word is not sent for an AI answer. When a word is not in your list it says so, and you can allow a single AI lookup without turning the mode off. In normal mode only the word and its sentence go out, and the picture is read on your Mac and thrown away. Details are on the privacy page. For the everyday shortcut, see looking up a word on Mac, and if Look Up misbehaves, Look Up not working.

Questions people ask

How do I add a Spanish dictionary to my Mac?
Open Dictionary, choose Dictionary, then Settings, and tick the Spanish sources. Apple's guide names Spanish dictionaries as an example. Wait for the download to finish, then drag the source up if you want it to answer first.

Is there a Japanese dictionary built into the Mac Dictionary app?
As of November 2026 the Dictionary source catalogue on macOS 26.5 includes Sanseido Super Daijirin and the Sanseido Wisdom English-Japanese and Japanese-English dictionary. Tick them in Dictionary, Settings.

How do I add a medical dictionary to my Mac?
Apple does not ship one in the catalogue read for this page. You can look for a third-party .dictionary file and put it in ~/Library/Dictionaries, though many old download sites are gone. Abbreviations need context, which is why LeafyApp reads the surrounding sentence.

How do I change the dictionary language on a Mac?
There is no single switch. Tick the dictionaries you want in Dictionary, Settings, and drag them into the order you want them to answer. The top ticked source that has the word answers first.

For the languages and fields Apple does not cover.

Free while LeafyApp is in beta. One download, macOS 14 and up.

Download for Mac

Also worth a look: looking up a word on Mac, medical abbreviations lookup, or Look Up not working on Mac.