An Etymological Dictionary of Astronomy and Astrophysics

1. The first letter of the Hebrew alphabet (ℵ).
   

2. A → cardinal number representing an uncountable set. For example, ℵ₀ (pronounced aleph-null, aleph-nought, or aleph-zero) is the smallest infinite cardinal and ℵ₁ is the smallest cadinal larger than ℵ₀.

See also: Hebrew and Phoenician letter, from Semitic languages.