1O or 1-O or 1º (the digit "1" and the letter "O") may refer to:
1º Sector, the primary sector of the economy 2017 Catalan independence referendum, called for 1 October 2017, known as 1-O
See also
1º de Mayo (disambiguation) 10 (disambiguation) (the digit "1" followed by the digit "0") I0 (disambiguation) (the letter "I" followed by the digit "0") IO (disambiguation) (the letter "I" followed by the letter "O") O1 (disambiguation) (the letter "O" followed by the digit "1") First officer (disambiguation) Primo (disambiguation) Glucogallin, or 1-O-galloyl-beta-D-glucose Isomalt, or 1-O-alpha-D-glucopyranosyl-D-mannitol Corilagin, or Beta-1-O-galloyl-3,6-(R)-hexahydroxydiphenoyl-d-glucose