Thine is defined as something belongs to you.(pronoun)
An example of thine is John telling Mary that the horse belongs to John, by saying the horse is thine.
See thine in Webster's New World College Dictionary
Origin: ME thin < OE, gen. of thu, thou (ME loss of -n before a consonant gives thy)
possessive pronominal adjective
See thine in American Heritage Dictionary 4
pron. (used with a sing. or pl. verb)
Origin: Middle English thin; see thy.
Learn more about thine