[SAJ]

Sorry, the word 'octopus' is entirely Latin in its etymology. 'Octo' = Latin for 'eight', 'pus', derivation from 'pes' = Latin nominative singular for 'foot'.

[FreedomCalls]

You are flat out wrong. No less a source than the authoritative Oxford English Dictionary gives this:

octopus

  • noun (pl. octopuses) a mollusc with eight sucker-bearing arms, a soft body, beak-like jaws, and no internal shell.

  — DERIVATIVES octopoid adjective.

  — USAGE The standard plural in English of octopus is octopuses. However, since the word comes from Greek, the Greek plural form octopodes is still occasionally used. The plural form octopi, formed according to rules for Latin plurals, is incorrect.

  — ORIGIN Greek, from okto ‘eight’ + pous ‘foot’.