Trefethen rhymes with:
anthon, blethen, bothun, brethen, cauthen, cauthon, cawthon, donathan, dothan, earthen, elizabethan, ethan, johnathan, johnathon, jonathan, jonathon, jonothan, kathan, lathan, lathon, laythan, lecithin, lengthen, leviathan, louthan, mathan, mcclenathan, mcglothen, mcglothin, mckeithan, mckeithen, mckethan, midthun, mithun, mothon, nathan, pathan, ramthun, snethen, strengthen, swaminathan, trevathan, warthen, wathen, witthuhn, worthen
Trefethen sounds like:
tarbutton, trafton, trepidation, trevathan