septenary(n = noun.quantity) 7, heptad, septet, seven, sevener, vii - the cardinal number that is the sum of six and one;
is a kind of digit, figure

1.  Consisting of, or relating to, seven; as, a septenary number. I. Watts. [1913 Webster]

2.  Lasting seven years; continuing seven years. Fuller. [1913 Webster]

   The number seven. Holinshed. [1913 Webster]

septenary, adj. & n.
--adj. of seven, by sevens, on the basis of seven.
--n. (pl. -ies)
1 a group or set of seven (esp. years).
2 a septenarius.

Etymology:
L septenarius (as SEPTENARIUS)