tier in WordNet English dictionary

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