18O or variant, may refer to:
Oxygen 18 (18O), an isotope of oxygen with atomic mass number 18 (8 protons + 10 neutrons) 2019 Catalan general strike (18-O) 18º, a way to write the ordinal number 18th (eighteenth)
See also
δ18O
O-18 (disambiguation) and O18 18 (disambiguation) O (disambiguation) 180 (one-eight-zero; 180) I80 (disambiguation) (i-eight-zero; I80) l80 (disambiguation) (L-eight-zero; l80)