Those in whom the Greek word lives only while they are hunting for it in the lexicon, and who then substitute the English word for it, are not reading Greek at all; they are only solving a puzzle.
C.S. Lewis, Surprised by Joy. (A longer quotation is here.)
To read the New Testament fluently in Greek is one of my ambitions, an ambition I am actively pursuing. The more I learn about New Testament Greek, however, the more I see errors and problems where people have relied on brief entries in Greek-English dictionaries in explaining certain Bible words and passages. This is especially true if older dictionaries are used that were written before the discoveries, in the 1800s and 1900s, of numerous ancient papyri written in Koine Greek.
Even if the definitions in these dictionaries accurately provide a range of the possible meanings of a given Greek word, they usually do not provide adequate information as to how the word was used by the original speakers and authors. For example, a phrase such as kalon ergon (which can be translated as “a good deed” or “a fine work”, etc) has a significance that may differ depending on the context (e.g., Mark 14:6 cf. 1 Tim 3:1 NIV).
Knowing the dictionary definition of a particular Greek word and its grammar is useful but sometimes this is not enough information to gain an understanding of how and why that word (or a phrase) was used in a particular sentence or by a particular author.
A dictionary definition does not always give the sense the author intended. It does not alert us to any rhetorical devices being used, devices such as hyperbole or irony. And it may not note the use of idioms. Moreover, information about the etymology of words, which is included in some dictionaries, can mislead people about how the words were used and what they meant in real life.
A knowledge of the Greek literature and documents that were written around the same time as when the New Testament was written, as well as a knowledge of early Jewish and Greco-Roman cultures, are important in helping our understanding of New Testament Greek.
I like what Wayne A. Meeks says on this topic:
… so simple a task as translating a sentence from an ancient language into our own requires some sense of the social matrices of both the original utterance and ourselves. When we take up the dictionary and grammar to aid us, we err unless we understand that they only catalog the relics of language as a fluid, functioning social medium. If we translate without that awareness, we are only moving bones from one coffin to another.
Meeks, The First Urban Christians: The Social World of the Apostle Paul, Second Edition (Yale University Press, 2003), 5.
We need to be careful that our use of Greek dictionaries and other aids is truly helping us to see the living Word of God more authentically and that we are not using them to “move dead bones.”
Learning New Testament Greek takes a long time and is an ongoing process, and most people do not have the time or inclination to embark on this venture. Nevertheless, if you do want to find out possible meanings of a Greek word, be aware that Strong’s and Vine’s are not reliable dictionaries. But if you do use Strong’s or Vine’s, or any dictionary, read the instructions on the first few pages about how to use them properly.
Using a dictionary is the first step in understanding the meaning of a word, not the final word. And we should avoid being presumptive or pedantic about ascribing meanings and functions to certain Greek words and phrases that may be unclear and ambiguous to modern readers.
I love reading the New Testament in Greek. The New Testament is more authentic and seems more vivid in Greek than in English, but I have to keep reminding myself to take it slowly and carefully, and not to rush to conclusions about definitions and interpretations.
It is no wonder Greek students are cautioned that “A little Greek is a dangerous thing.”
 Seumas McDonald has a tiny post about why we must read non-New Testament Greek to understand New Testament Greek here.
 If you can’t read Greek and want to find out the scope of meaning of a certain passage, read the passage in several English translations. I recommend the (1) Christian Standard Bible, (2) New Revised Standard Version, and the (3) Common English Bible. Most well-known English translations are excellent. And read the whole book or letter that contains the passage, looking for keywords and themes. Context!
 Strong’s Concordance (first published in 1890) is not always accurate. Strong’s is a wonderful work, but it was written and published around the same time as the numerous newly-discovered Greek papyri in Egypt were beginning to be published and discussed. The newly discovered papyri have greatly helped us to better understand the Greek of the New Testament.
George Milligan has written about the value of these papyri in his “General Introduction” to the dictionary he produced with J.H. Moulton, The Vocabulary of the Greek Testament: Illustrated from the Papyri and Other Non-literary Sources (London: Hodder & Stoughton, 1929), vii-xx. This can be read here.
 For example, the italicised English words in Strong’s (not counting the pronunciation guide) are not to be taken as definitions of the given Hebrew or Greek word. Rather, they are every rendering of that word in the King James Bible, and some of these renderings involve compromises, as is always the case in any translation from one language to another. The words following these italicised words are definitions, but some are not as accurate as they could be.
Furthermore, I’ve seen novices make errors because they haven’t understood that Strong’s, and most Greek-English dictionaries and lexicons, usually only provide information on the lexical forms of nouns, verbs, and adjectives and not on words in their inflected forms.
Postscript: September 1, 2021
John H. Walton echoes Meek’s point about understanding the social matrices behind a language. Writing about biblical Hebrew, Walton urges his students to “enter the culture.”
When people want to study the Bible seriously, one of the steps they take is to learn the language. As I teach language students, I am faced with the challenge of persuading them that they will not succeed simply by learning enough of the language to engage in translation. Truly learning the language requires leaving English behind, entering the world of the text and understanding the language in its Hebrew context without creating English words in their minds. They must understand Hebrew as Hebrew text. This is the same with culture. We must make every attempt to set our English categories aside, to leave our cultural ideas behind, and try our best (as limited as the attempt may be) to understand the material in its cultural context without translating it.
Walton, The Lost World of Genesis One (Downers Grove, IL: IVP Academic, 2009), 9.
Postscript: January 13, 2022
I do not recommend the new Cambridge Greek Lexicon for students of the New Testament. This lexicon was written with students of Classical Greek in mind. The lexicographers did not consult the Septuagint, Jewish authors writing in Greek (e.g., Philo and Josephus), or inscriptions or papyri. These post-classical sources shed light on New Testament Greek. The Cambridge Greek Lexicon does not cover the New Testament itself apart from the four Gospels and Acts.
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