Many questions can be easily answered by searching for a word, phrase, or idiom in a free online dictionary. Meaning, pronunciation, and even some grammar questions (such as which preposition is the most appropriate after a specific verb) are all covered in most dictionaries.
To prevent our site from duplicating this information, we expect that users check at least one dictionary before posting a question. To make this easier, we've created a "List of Resources" below of a few popular dictionaries and the differences between them. Feel free to use resources that aren't on this list or even cross-reference several of them (but make sure that your sources are reputable!); the more solid your research is, the more likely your question is to be well received. Once you've consulted your dictionary (or several), if your question wasn't satisfactorily answered there, include a link to the dictionary entry and explain why it didn't answer your question.
If you are a non-native speaker, consider asking on ELL instead. While ELL has a similar requirement for research, everything about it is tailored toward answering non-native questions.
Additionally, be sure to search for duplicates before asking. If you did find a question that looked promising but only had bad answers, you can still ask your question if you link to the old one and explain why those answers don't work for you. Note: Finding duplicates on this site can be tricky, so it's OK if a question ends up being closed as a duplicate.
List of resources
These dictionaries were selected from our larger list because they are free, reputable, and easy to use.
- Cambridge Dictionaries Online (CDO) — The main dictionary ("English") is British-focused, but includes definitions and sound clips for American English as well. Some of the entries have pictures. Additionally, there are two more dictionaries, one for each dialect: "Essential American English" and "Essential British English". Unlike other American dictionaries, the pronunciation system is IPA.
- Collins — Several dictionaries on the same page, with the first one being primarily British. American English is covered somewhere further down on the page, though (unlike other American dictionaries) the pronunciation system is IPA. Some of the entries have pictures, and in addition to sound clips, there are videos of people pronouncing each word. Also covers the etymology (somewhere).
- Merriam-Webster (MW) — An American dictionary, with some British (or World English) definitions. Has sound clips for how to pronounce words. No IPA. Includes etymology.
- Dictionary.com — The primary dictionary is American English, with sound clips. Features both phonetic respelling and IPA transcriptions. Some entries include content above and beyond that from other sources.
A learner's dictionary is a type of dictionary with additional features that are geared towards non-native speakers. For example, many nouns will be marked as "countable" or "uncountable" whereas a general dictionary would not have either label unless it was a particularly rare word.
Idioms, expressions and slang
Most dictionaries define idioms, either as their own entry or under a headword. For example, I searched for horse to water in the search box, and Collins returned their entry for you can lead a horse to water but you can't make it drink
TFD Idioms and Phrases — I found that searching for idioms and phrases in a dedicated dictionary like this one was easier than searching in a general-purpose dictionary.