(physics) A minor stable isotope of calcium, ⁴³₂₀Ca, having twenty protons and twenty-three neutrons; it amounts to about 0.1% of the element in nature

(politics) Currently ruling; being the present controlling authority, as of a government or country.

(nautical, military) the Argentine Navy (Armada de la República Argentina)

(attributive) Relating to temperatures below one millikelvin.