'rt

'rt (clitic)

1. (archaic) Contracted form of art; only used in thou'rt.
   • 1893, Norman Gale, “To a Glow-Worm”, in Orchard Songs, London: [Charles] Elkin Mathews & John Lane; New York, N.Y.: G. P. Putnam’s Sons, →OCLC, page 100:

     Here at this cherry’s grassy base / Thou ’rt sure of no upbraiding; / Too small thy lantern to arouse / The thrush for midnight raiding.