The word 'thee' originates from the Old English 'þē', which served as the singular object case (accusative and dative) of the second person pronoun. It is part of the ancient Germanic pronoun system, derived from the Proto-Germanic þek, which in turn traces back to the Proto-Indo-European tege, a form of the second person singular pronoun. As English grammar simplified, the distinct subject ('thou') and object ('thee') forms of the second person singular fell out of common use, largely replaced by the all-purpose 'you'. 'Thee' survives primarily in historical, religious, poetic, and some regional dialectal contexts.

This is a simplex word, a direct descendant from Old English 'þē', the accusative and dative singular form of the second person pronoun.