romantic describes what belongs to love and courtship, and equally what belongs to the imagination rather than to fact — idealized, heightened, and not quite answerable to the world as it is.
The word carries two families of meaning that most speakers move between without noticing the seam. The first is affectional — a romantic dinner, a romantic partner, anything belonging to courtship or to 📝love of the pair-bonded kind. The second is dispositional and faintly skeptical: a romantic view of history, a romantic notion of the frontier, a founder who is romantic about how fast a business will grow. Here the word marks a preference for the imagined over the observed, and it lands as affection or as quiet accusation depending on who is speaking. Capitalized, it names the Romantic movement in European art, literature, and music, which set feeling, nature, and individual imagination against neoclassical order.
The route into English runs backwards through literature rather than through feeling. The adjective arrives in the 1650s from French romantique, built on Old French romanz — a verse narrative told in the vernacular rather than in Latin, ultimately from the Vulgar Latin phrase romanice scribere, "to write in a Romance language." The sense of an ideal love affair appears only in the 1660s, and the sense of poetic or inspiring scenery by 1705. The love meaning is therefore downstream of the storytelling one: to call a thing romantic was first to say it resembled the marvelous events of a romance.
Romantic is not a synonym for sexual, and the distinction does real work in relational vocabulary — 📝platonic love is close and non-sexual, while a bond can be romantic without being sexual, or sexual without being romantic. Nor is it a synonym for sentimental, which indulges feeling rather than idealizing vision.