Y

(LETTER) (plural Y's or Ys), y (plural y's or ys) [noun] [C] - the 25th letter of the English alphabetA Y-chromosome is a sex chromosome that exists only in male cells.If a Y-chromosome combines with an X-chromosome during fertilization, a male baby will result.(UK trademark) Y-fronts are a piece of underwear for men and boys, covering the area between the waist and the tops of the legs, which have an opening at the front which is the shape of an upside-down Y.