From Middle English thy, thi, apocopated variants of Middle English thine, thyn, thin, from Old English þīn, from Proto-Germanic *þīnaz, from Proto-Indo-European *téynos (“thy; thine”), from Proto-Indo-European *túh₂ (“thou”). See thou.
- (archaic, literary) The possessive form of thou: that belongs to thee; that belongs to you (singular).
From Middle English thy (“because, forwhy”), shortened form of for-thy, forthy (“for that”), from Old English for þȳ [þe] (“because [that]”) from for (instrumental preposition) + þȳ (“by that”), instrumental case of þæt. More at the, that.
- (obsolete) because.