σου [144 verses](pron 2nd sg gen) "Thy" is sou is the genitive form of the second-person, singular pronoun that means "of you" and "your." As a genitive object of a preposition, as here, it means a movement away from something or a position away from something else.  -- The word translated as "your" is the genitive form of the singular, second-person pronoun, which is most commonly the possessive form.  This pronoun follows the noun so "of yours."