The word "sternoid" is spelled with an "o" instead of an "e" because it is derived from the Greek word "sternon," which means breastbone. The "o" in "sternoid" represents the Greek letter omicron (ɔ), which is pronounced like the "o" in "cot." The "e" in "sternum," which refers to the breastbone itself, represents the Greek letter epsilon (ɛ), which is pronounced like the "e" in "met." Therefore, "sternoid" is pronounced /'stɜː.nɔɪd/ (STER-noyd), while "sternum" is pronounced /'stɜː.nəm/ (STER-num).