Walter Ewing Crum assembled a vast amount of information on the vocabulary of Coptic. His 1939 compilation continues to be the standard reference work in this field.
However, Dr. Crum worked at a time when it could still be taken for granted that all students of ancient languages were thoroughly versed in Greek and Latin. There are an enormous number of examples glossed only in Greek (and then commonly with abbreviations instead of full Greek words). So be prepared to look up a lot of Greek words, unless you have a good knowledge of this language already. (A hint to prospective students: Coptic uses a large number of Greek loanwords, so you are well advised to have some knowledge of Greek before taking up Coptic in any event.)
Another frustrating feature of Crum is that many examples are given in Coptic with no translation at all. Sometimes he gives a biblical reference, so if you look it up in a Bible you can see the meaning in the context Crum intended.
Crum alphabetized Coptic taking into account only consonants to begin with. Only when you have identical consonants in two or more words are vowels taken into account. They are listed in Greek alphabetical order. Words that have no final vowel come before words that do have a final vowel. Crum's treatment of the sequence OY seems somewhat unpredictable. This combination sometimes functions as a consonant (when next to vowels) and sometimes as a vowel (when between consonants), and Crum generally seems to alphabetize accordingly. However, sometimes he seems to arbitrarily alphabetize a consonantal use as if it were a vowel or vice versa. This can lead to considerable frustration for the user of his lexicon.
For a quicker reference for most vocabulary, consult Richard Smith's A Concise Coptic-English Lexicon, 2nd ed. Smith gives no examples, so it is far easier to find vocabulary items without wading through page after page of mind-numbing details. You can consult Crum for more details on a word's usage, if necessary. Smith's modern English is often clearer than Crum's rather antiquated variety. The best reference for the many varying forms of stems in Coptic words is found in the large glossary in Thomas O. Lambdin's Introduction to Sahidic Coptic.
It should be noted that Crum covers all the dialects of Coptic that had been identified at the time he wrote (more have been identified in later years), while Smith and Lambdin only deal with Sahidic. However, Sahidic is the dialect that students normally begin with, so Smith and Lambdin's focus on this dialect is not a problem.
Crum includes helpful indexes of English, Greek and Arabic words used in his definitions. However, his choice of glosses is, as I indicated above, rather archaic. So if you go to look up the words "peasant" and "farmer" in his English index, you will not find them. Instead, you have to look for "husbandman" or "cultivator". On the other hand, neither Smith nor Lambdin give any English index to their work. Better Crum's than none!
One final detail has to do with the Greek used in Coptic. Both Crum and Smith carefully avoid listing any of the thousands of Greek words to be found in Coptic manuscripts. Lambdin includes a brief list of the Greek used in the reading selections he includes in his book. The closest thing to a real dictionary of Coptic Greek that I have found is the very expensive Coptic-German work Worterbuch Der Griechischen Worter in Den Koptischen Dokumentarischen Texten (Dictionary of the Greek Words in the Coptic Documentary Texts). This only covers documentary texts, though, such as business and government documents, not literary texts, such as the theological works commonly studied by students of Coptic. To somewhat make up for this lack, you can use Liddell & Scott's A Greek-English Lexicon, Ninth Edition with a Revised Supplement. However, the sense in which a word is used in Coptic may not always be found in L&S, or it may be buried in a long list of senses; you just have to do your best with the tools at your disposal. With experience it gets easier.
The Wipf & Stock edition of Crum offered here seems to be printed with a slight reduction of the type size from the original. Even this slight reduction makes it noticeably harder to read. If you can get hold of an older Oxford printing, by all means do so. The content of the dictionary has not changed one iota. The only appreciable addition to this edition is a modern introduction by James M. Robinson. The original edition is decidedly more legible.
