Abarim Publications' online Biblical Greek Dictionary
The adjective ευθυς (euthus) means straight. It's used for lines that don't digress but also for people who speak outright and without reserve. Whether that's always virtuous is not addressed by this word, although the opposite (speaking with hidden intent or shifting allegiances) is often not (Acts 8:21). Unlike in English, in Greek there is not a strong association between literal and moral straightness — because frankly, being morally "straight as an arrow" or otherwise "crooked as a Virginia fence" doesn't really make a whole lot of intuitive sense.
A much stronger association with straightness within the Greek language is that of clarity and unthwarted display. When Isaiah called for a path to be made straight (Matthew 3:3), and the Lord sent Ananias to look for Paul on Straight Street (same word; Acts 9:11), the narrative currency was not one of moral virtue but rather one of revelation, of liberation and of coming out. Also note that the Greek uses the plural form of the adjective, which suggests that not the road was to be made straight (as Isaiah may have originally meant), but rather the addressed makers (literally: you be straight in making the road ...).
This adjective is used a mere 8 times in the New Testament, see full concordance, but from it derive:
- The adverb ευθεως (eutheos), meaning straight or straightly. This word occurs 88 times in the New Testament, see full concordance, but as often in the gospel of Mark as in the whole rest of the New Testament. Why Mark instilled such massive urgency in his account isn't immediately clear and subsequently much debated among scholars, but note that unlike our English equivalents, our Greek adverb has a very strong connotation of clarity, outrightness and laying it all out on the table. Our English translations may read that Jesus saw the heavens open immediately after emerging from his baptism in the Jordan (Mark 1:10), but to a Greek audience he saw the heavens open without any visual difficulty: as clear as glass, without distortion or having been relayed by angels or other agents. He saw heaven panoramically, live and direct.
- Together with the noun δρομος (dromos), meaning a track or course: the verb ευθυδρομεω (euthudromeo), meaning to travel a course without digression (Acts 16:11 and 21:1 only).
- The verb ευθυνω (euthuno), meaning to straighten, to make straight. In Greek this verb's primary meaning is strongly augmented with being openly and publically available, clearly visible without hidden agendas or small print. The "straight" highway of the Lord, which Isaiah famously called for (John 1:23), is not typically a highway without any bumps or bends, but a highway that everybody knows about and which has no hidden features. This verb is used only twice in the New Testament, the other occurrence being in James 3:4, and from it in turn derives:
- The noun ευθυτης (euthutes), meaning straightness, openness, candidness; having no hidden agenda or considerations (Hebrews 1:8 only).