(physics) A minor stable isotope of chromium, ⁵⁴₂₄Cr, having 24 protons and 30 neutrons; it amounts to about 2% of the element in nature

(physics) A minor stable isotope of iron, ⁵⁴₂₆Fe, having 26 protons and 28 neutrons; it amounts to about 6% of the element in nature

(sports) The act of spinning 540 degrees in the air, making 1½ turns.

plural of 540