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Dictionaries you buy once.

Buy Dictionary and Thesaurus Pro. It is the best-reviewed of these by a clear margin, it works with no signal, and it carries a thesaurus too. Merriam-Webster is the one to buy if the name on the definition matters to you. LDOCE is for people learning English rather than people who already speak it, and Roget's II is a specialist thesaurus with an interface to match its age.

The filter. Every app here is a single purchase. None of them can start charging you monthly for what you already bought. See every app under this rule ›
Top pick

Dictionary and Thesaurus Pro

Farlex, Inc.
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$9.99 once4.9★ (2,562)Updated Apr 2, 2026
Verdict
The highest-rated reference app on the store, and the only one here where nobody in two hundred recent reviews had a complaint worth clustering.
Best for
Anyone who looks words up often and wants it to work on a plane, in a tunnel, or with the data off.
The catch
It is the paid version of a dictionary that is already free with adverts. What you are buying is the ads removed and the content stored on the device — useful, but not new words.
One-time purchaseWorks offlineNo adsThesaurus

Merriam-Webster Dictionary+

Merriam-Webster, Inc.
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$9.99 once4.8★ (22,098)Updated Jul 29, 2026
Verdict
The one with the name on it. If you want the definition that settles an argument, this is the dictionary people mean.
Best for
Someone who cares which dictionary a definition came from.
The catch
Five of the last two hundred reviews report it crashing on launch after signing in, and others describe the app pushing them toward subscription services they had not asked for.
One-time purchaseWorks offlineApple Watch

English Dictionary - LDOCE PRO

Nguyen Thi Hoai Thu
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$14.99 once4.7★ (2,208)Updated Oct 3, 2025
Verdict
A learner's dictionary rather than a native speaker's: definitions written in deliberately simple language, with the pronunciation work that implies.
Best for
Someone learning English who needs the definition itself to be readable.
The catch
The most expensive here, and reviewers dispute how much of it truly works offline — a few say the offline content they paid for was not there, and others that an update made it slow.
One-time purchaseLearner's definitionsPronunciation

Roget's II: New Thesaurus

Enfour, Inc.
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$4.99 once4.7★ (363)Updated Aug 28, 2026
Verdict
A real thesaurus rather than a dictionary with synonyms bolted on, carrying Roget's alongside Moby's two and a half million entries.
Best for
A writer hunting for a word who wants breadth over a tidy interface.
The catch
It looks and behaves its age. Six of the last two hundred reviews call it unusable, describing results dumped into one window of tiny text with no way through them.
One-time purchaseThesaurus onlyVery large

Side by side.

AppPriceWorks offlineThesaurusSourceUpdated
Dictionary and Thesaurus Pro$9.99YesYesTheFreeDictionaryApr 2, 2026
Merriam-Webster Dictionary+$9.99YesYesMerriam-WebsterJul 29, 2026
English Dictionary - LDOCE PRO$14.99DisputedNoLongmanOct 3, 2025
Roget's II: New Thesaurus$4.99YesOnlyRoget's, MobyAug 28, 2026

Who should skip this entirely.

iOS has a dictionary built in — select any word, tap Look Up, and it is there, offline, for nothing. For most people that is the end of the question. These are worth paying for when you want a specific publisher's definitions, a proper thesaurus, or a learner's dictionary written in simpler English than the built-in one uses.

Questions.

Is the built-in iOS dictionary any good?Yes, and it is free. It draws on the New Oxford American Dictionary and works offline. Buy one of these when you want a different publisher, a real thesaurus, or learner-level definitions.
Which of these works with no signal?All of them claim to. Reviewers only dispute it for LDOCE, where several say the offline content they paid for was missing.