Y, y

noun, plural Y’s or Ys, y’s or ys.

1. the 25th letter of the English alphabet, a semivowel.
2. any spoken sound represented by the letter Y or y, as in yet, city, or rhythm.
3. something having the shape of a Y.
4. a written or printed representation of the letter Y or y.
5. a device, as a printer’s type, for reproducing the letter Y or y.

1. yoctosecond.

noun

1. one septillionth (10-24) of a second. Abbreviation: ysec, ys

1. The symbol for yttrium.