In each of the ten cases with zero or unit mass, the finite part of the scalar 3-loop tetrahedral vacuum Feynman diagram reduces to four-letter "words" that represent iterated integrals in an alphabet of seven "letters" . There are 7^4 such four-letter words, but only two of these are primitive terms. Defining U | = | integral_0^1 (d x_1)/x_1 integral_0^(x_1) (d x_2)/x_2 integral_0^(x_2) (d x_3)/(-(1 + x_3))× integral_0^(x_3) (d x_4)/(1 - x_4) sum_(0