1) Based on the number six 2) In base 6 3) Like a six-year celebration 4) Of six 
The senary numeral system (also known as base-6 or heximal) has six as its base. It has been adopted independently by a couple of cultures. Like decimal, it is a semiprime, though being the product of the only two consecutive numbers that are both prime (2,3) it has a high degree of mathematical properties for its size. As six is a superior highly...
involving or based on six; having a numerical base of six
• (a.) Of six; belonging to six; containing six.
Sen'a·ry adjective [ Latin senarius , from seni six each, from sex six. See Six .] Of six; belonging to six; containing six. Dr. H. More.