octa-, octo-, oct-, octi-, octon-

(Greek > Latin: eight, eighth)

octarchy
A government by eight rulers; an aggregate of eight tribal or petty kingdoms each under its own ruler: applied by some historians (instead of heptarchy) to the eight kingdoms reckoned by them to have been established by the Angles and Saxons in Britain.
octave
Octavia
Octavius
octavo
octennial
1. Occuring every eight years.
2. Lasting or taking eight years
octet
octette
octillion
octiparous
October
octodecimo
octodont
octogenarian
1. A person who is in her/his eighties.
2. A person who is eighty to eighty-nines years old.
octogynous
In botany, having eight pistils.