Finding the right Arabic dictionary can be difficult. First you have to decide if you need a dictionary for Classical (Quranic) Arabic, Modern Standard Arabic (used in newspapers and literature) or Colloquial Arabic (dialects; Egyptian Arabic, Moroccan Arabic, etc.). Trying to translate an Arabic text using the wrong dictionary can be very frustrating. Fortunately at least for Modern Standard Arabic and Classical Arabic, there are some excellent dictionaries available. As for Colloquial Arabic (Arabic dialects), you will have very limited options.
Let us know what your favourite Arabic dictionary is.
Modern Standard Arabic
The Hans Wehr Dictionary of Modern Written Arabic This Arabic-English dictionary is a must-have for anyone who is serious about learning Modern Standard Arabic. Using it requires a basic knowledge of Arabic, as the entries are not arranged alphabetically but by root word.
Al-Mawrid Dictionaries Al-Mawrid dictionaries are excellent dictionaries and are available in Arabic-English or Arabic-English/English-Arabic. Words are arranged alphabetically and Al-Mawrid provides synonyms in Arabic for each entry. For beginners and intermediate students.
Oxford Arabic Dictionary Another excellent dictionary is the Oxford Arabic Dictionary (Arabic-English/English-Arabic). Over 2,000 pages with more than 130,000 words and phrases and 200,000 translations. Essential for anyone learning Modern Standard Arabic.