Ystafellyddes, n. a chambermaid
Ystagiad, n. a suffocation
Ystagu, v. to suffocate, to choke
Ystang, n. a perch in measure
Ystalm, n. a good while
Ystalu, v. to form a stock
Ystalwyn, n. a stallion
Ystanc, n. a holdfast, a bracket, a wooden book. Ystanc ceffyl, a horse-block
Ystanciad, n. a bracketing
Ystancio, to stanch; to bracket