The Collaborative International Dictionary of English v.0.48:

Septenary \Sep"ten*a*ry\, a. [L. septenairus, from septeni seven
   each, septem seven: cf. F. sept['e]naire. See Seven. ]
   1. Consisting of, or relating to, seven; as, a septenary
      number. --I. Watts.
      [1913 Webster]

   2. Lasting seven years; continuing seven years. "Septenary
      penance." --Fuller.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Septenary \Sep"ten*a*ry\, n.
   The number seven. [R.] --Holinshed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

septenary
    n 1: the cardinal number that is the sum of six and one [syn:
         seven, 7, VII, sevener, heptad, septet,
         septenary]