The term LIBRAN'S BIRTHSTONE is an astrological reference to the birthstone of those born under the sign of Libra, which is the seventh sign of the zodiac. The crossword solution for this term is OPAL, a four letter word. OPAL is a mineraloid gemstone composed of hydrated amorphous silica and is known for its unique play of color. It is the traditional birthstone for October and is associated with love, passion, and desire.