'Ys' definitions:

Definition of 'Ys'

From: GCIDE

Y \Y\ (w[imac]), n.; pl. Y's (w[imac]z) or Ys. Something shaped like the letter Y; a forked piece resembling in form the letter Y. Specifically: (a) One of the forked holders for supporting the telescope of a leveling instrument, or the axis of a theodolite; a wye. (b) A forked or bifurcated pipe fitting. (c) (Railroads) A portion of track consisting of two diverging tracks connected by a cross track. [1913 Webster]
Y level (Surv.), an instrument for measuring differences of level by means of a telescope resting in Y's.
Y moth (Zool.), a handsome European noctuid moth {Plusia gamma}) which has a bright, silvery mark, shaped like the letter Y, on each of the fore wings. Its larva, which is green with five dorsal white species, feeds on the cabbage, turnip, bean, etc. Called also gamma moth, and silver Y. [1913 Webster]