tier (
http://definr.com/tier)
n 1: a relative position or degree of value in a graded group:
"lumber of the highest grade" [syn:
grade,
level]
2: any one of two or more competitors who tie one another
3: a worker who ties something [syn:
tier up]
4: something that is used for tying; "the sail is fastened to
the yard with tiers"
5: one of two or more layers one atop another: "tier upon tier
of huge casks"; "a three-tier wedding cake"