sixty-sixth I. \| ̷ ̷ ̷ ̷| ̷ ̷\adjective 1.: being number 66 in a countable series < the sixty-sixth day > — see number table 2.: being one of 66 equal parts into which something is divisible < a sixty-sixth share of the money > II. noun 1.: number 66 in a countable series 2.: the quotient of a unit divided by 66 : one of 66 equal parts of something < one sixty-sixth of the total >