sixteenth adj., n.

"one more than fifteen, twice eight, four times four; the number which is one more than fifteen; a symbol representing this number;" Middle English sixtene, from Old English sixtyne, from siex (see six) + -teen. Similar formation in Old Frisian sextine, Middle Dutch sestien, Dutch zestien, German sechzehn, Old Norse sextan.

The age of the gods is always sixteen. Sixteen represents the number of perfection, of plenitude. In man it is after the sixteenth year that the first elements of decay begin to appear, and when the moon reaches the sixteenth digit it begins to decrease. [Alain Daniélou, "The Myths and Gods of India"]

From Latin contracted form sexdecim, sedecim come Italian sedici, French seize.

word-forming element making ordinal numbers (fourth, tenth, etc.), Old English -ða, from Proto-Germanic *-tha- (cognates: Gothic -da, -ta, Old High German -do, -to, Old Norse -di, -ti), from PIE *-to-, also *-eto-, *-oto-, suffix forming adjectives "marking the accomplishment of the notion of the base" [Watkins].

Cognate with Sanskrit thah, Greek -tos, Latin -tus; Sanskrit ta-, Lithuanian and Old Church Slavonic to, Greek to "the," Latin talis "such;" Greek tēlikos "so old, of such an age," Old Church Slavonic toli "so, to such a degree," toliku "so much," Russian toliko "only;" also see -ed.