William Haliday (1788–1812) was an Irish language enthusiast. He sometimes used a Gallicized version of his name William O'Hara, in some documents his surname is misspelt Halliday.
- Occupation
- grammarian
- Citizenship
- Kingdom of Ireland, United Kingdom of Great Britain and Ireland, Kingdom of Great Britain
- Born
- 1788
- Died
- 1812