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
- Catalan independence referendum, 2017
- 1º (disambiguation) Meaning "1st" in Italian and Spanish
- 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)
|This disambiguation page lists articles associated with the same title formed as a letter-number combination.
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