/ tɪə(r); NAmE tɪr/ noun
1.
a row or layer of sth that has several rows or layers placed one above the other :
a wedding cake with three tiers
The seating is arranged in tiers .
2.
one of several levels in an organization or a system :
We have introduced an extra tier of administration.
a two-tier system of management
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WORD ORIGIN
late 15th cent.: from French tire sequence, order, from tirer elongate, draw.