Decenarian maths are places of work and study for Avout who have vowed to remain inside for a ten-year interval. Apert for a Decenarian math occurs once every decade and is the time when most Avout join or leave the math.

Avout who have remained in a Unarian math for ten years may graduate to a Decenarian math.

"Tenner" is a slang term for both the Decenarian math itself and for for an Avout belonging to one.

Most of the avout protagonists of Anathem are Decenarians, Erasmas included.