tridecennary

tridecennary (not comparable)

1. (obsolete, rare) Of or pertaining to the number thirteen
   • 1856, William Robertson, The History of the Discovery and Settlement of America:

     The order of days in every month was computed, according to him, first by what he calls a tridecennary progression of days from one to thirteen, […]

• John A. Simpson and Edmund S. C. Weiner, editors (1989), “tridecennary”, in The Oxford English Dictionary, 2nd edition, Oxford: Clarendon Press, →ISBN.