1O
1O or 1-O (the digit "1" and the letter "O") may refer to:
1o Sector, see Primary sector of the economy
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
2017 Catalan independence referendum, called for October 1, 2017, known as 1-O