The cardinal number that is the sum of seven and one

• Crew, not counting the cox, perhaps
• Oxygen atom's protons, e.g
• Oars in a quad scull, e.g
• Series of eight
• Two foursomes
• Rowing team, e.g
• Rowing group
• Slices in a pizza, often
• Pizza slices, often

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Octad \Oc"tad\, n. [Gr. ?, ?, the number eight.] (Chem.) An atom or radical which has a valence of eight, or is octavalent. A group of eight things.