- octal system
- octamer
- octamethylcyclotetrasiloxane
- octane
- octane number
- octane number; octane value; octane rating
- octane rating
- octane value
- octangular
- octanoic acid
- octanol
- Octans
- octant
- octant rule
- octaose
- octatetracontagon
- octavalent
- Octav Bancila
- octave
- Octave Chanute
- Octavia
- OCT Contemporary Art Terminal
- octdong surface
- octet
- octet breaking