Onos - oh'noss - n. - A Greek concept of rational worry; represented by Homer's Odyssey in Athena, a Greek Goddess, and many Greek heroes in other traditional works, it is considered a positive attribute.
Romans considered "onos" a negative attribute, like Odysseus' intelligence, and it became transmuted into the less-positive "onus," or "burden."

The big giant alein in natural selection it can pwn marines by eating them its pretty much unstopable if you dont have any weapon upgrades.

Same as "Oh No", but delivered in a more sarcastic, or comedic fasion.