Lexicons are some of the most helpful tools in one’s study, particularly when striving to understand how a word or phrase was originally used, and what it might’ve originally meant in a given context.
For Greek lexicons, most folks will say you need BDAG. And you do, it really is the first place you should go when looking deeper into words found in the Greek New Testament. But there are other lexicons too. One that is an excellent supplementary lexicon is Ceslas Spicq’s Theological Lexicon of the New Testament (TLNT), translated (from the original French into English) by James D. Ernest. The TLNT is not exhaustive (it does not treat every word found in the Greek NT), but its entries are helpful and substantive.