one-hundred-millionth adjective 1noun 1forms 1 adjective1 •The ordinal form of the number one hundred million. noun1 •One of one hundred million equal parts of a whole.The invention consists of a thin film covered with regularly spaced holes measuring about 100 angstroms in diameter, or about one one-hundred millionth of a meter. — 1989 formsone-hundred-millionths
