The Collaborative International Dictionary of English v.0.48:
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
(b) A forked or bifurcated pipe fitting.
(c) (Railroads) A portion of track consisting of two
diverging tracks connected by a cross track.
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