octo- Also octa-.
Eight; having eight.
[Latin octo or Greek oktō, eight.]
Words in octo- are usually of Latin origin, ones in octa- from Greek. An octopus has eight arms; the month of October was originally the eighth month of the Roman year; an octuple consists of eight parts or things; an octocentenary is the eight-hundredth anniversary of a significant event; an octave is a series of eight notes occupying the interval between (and including) two notes, one being half the frequency of the other; an octagon is a plane figure with eight straight sides and eight angles; an octahedron is a three-dimensional shape having eight plane faces. Octogenarian, a person in their eighties, derives from Latin octoginta, eighty.