tier 1 
(tîr)
(tîr)n.
1. One of a series of rows placed one above another: a stadium with four tiers of seats.
2. A rank or class.
tr. & intr.v. tiered, tier·ing, tiers
To arrange (something) into or rise in tiers: tier a wedding cake; balconies that tier upward.
[Middle English tire, row, rank, from Old French, from tirer, to draw out; see TIRADE.]