Vine's Complete Expository Dictionary of Old and New Testament Words for me is second best to the Concordence. I've purchase several Bible dictionaries over the years and was not as pleased as I was after purchasing Vine's.
If you are looking to gain better understanding of Gods word through greater definition and understanding of the original language, this book will help. You do not need to be a Greek scholar to use this tool of knowledge, looking up words in English, being given the Greek used in the original text of scripture and a summery meaning in relation to it's use in the text along with variances of the word. With this book you will come to a greater knowledge of Gods word. I would have given 5 stars but their is one small misprint in the book under long suffering, Greek word Makrothumeo, in the Greek word one letter is missing in the middle of the word, if you study Greek you may notice it.