Thine is an old English word meaning “yours.” You'll find it in older texts like Shakespeare's plays or the King James Bible, where people might say “The kingdom is thine” instead of “The kingdom is yours.”

The word appears in formal or poetic contexts, especially when the next word starts with a vowel sound. While “thy” (meaning “your”) was used before consonants, thine was used before vowels: “thy book” but “thine apple.” Think of it like how we say “a book” but “an apple.”

When you read historical literature or religious texts, you might encounter phrases like “Thine eyes” or “The glory is thine.” Today we only use thine when quoting old texts or creating a deliberately old-fashioned effect.