Abbreviation of uranium-235.

(physics) A fissile isotope of uranium, used for energy generation and in atomic weapons, containing one hundred and forty-three neutrons. It has a half-life of 7·038×10⁸ years; it decays into thorium-231 and ultimately lead.

(physics) A rare stable isotope of neon, ²¹₁₀Ne, having ten protons and eleven neutrons; it amounts to less than 0.3% of the element in nature

(physics) The major stable isotope of neon, ²⁰₁₀Ne, having ten protons and ten neutrons; it amounts to over 90% of the element in nature

(physics) A minor stable isotope of neon, ²²₁₀Ne, having ten protons and twelve neutrons; it amounts to about 9% of the element in nature

(physics) The only stable isotope of sodium, ²³₁₁Na, having eleven protons and twelve neutrons

(physics) The major stable isotope of magnesium, ²⁴₁₂Mg, having twelve protons and twelve neutrons; it amounts to about 79% of the element in nature

A timekeeping convention in which the 24 hours of the day are treated as a single period, rather than two sets of 12 hours.

(idiomatic) In hindsight things are obvious that were not obvious from the outset; one is able to evaluate past choices more clearly than at the time of the choice.

(telecommunications, computing) Recommended Standard 232; the standard for serial binary signals between a DTE and a DCE.