Greek erōs (ἔρως) — passionate, desiring love, especially between man and woman. The word does not occur in the NT text at all — a striking absence. The Septuagint uses it occasionally (e.g., Proverbs 7:18, 30:16). Plato developed it philosophically as the soul's longing for the Beautiful and the Good; this became central to Christian mystical writers (Pseudo-Dionysius, Bernard of Clairvaux). In ordinary Greek, erōs covers everything from sexual passion to the highest spiritual yearning. C. S. Lewis's The Four Loves treats it as "being in love" — the enchantment, the beholding, the compulsive desire for the specific beloved.
The NT's silence on eros is sometimes misread as an anti-eros stance. It is not. The NT has other terms for married love — Paul's instructions in 1 Corinthians 7 and Ephesians 5, the Song of Songs' celebration of erotic delight between husband and wife, the Proverbs 5 exhortation to "rejoice in the wife of your youth... be intoxicated always in her love." The Christian position on eros is: contained within marriage, it is holy, good, and a creational gift; outside marriage, its fire consumes (Proverbs 6:27-28). Modern culture has inverted the equation — treating eros as autonomous and sovereign rather than ordered. Benedict XVI's encyclical Deus Caritas Est (2005) argued that eros must be purified and integrated with agape: "Eros and agape — ascending love and descending love — can never be completely separated... the two loves need each other." Rightly ordered eros is fierce, faithful, monogamous, fruitful, and self-giving. That is what Song of Songs celebrates. That is what marriage is for.