1. [n]  position 80 in a countable series of things
2. [adj]  the ordinal number of eighty in counting order

EIGHTIETH is a 9 letter word that starts with E.

1. \Eight"i*eth\, a. [From {Eighty}.]
   1. The next in order after seventy-ninth.
   
   2. Consisting of one of eighty equal parts or divisions.
   
   

2. \Eight"i*eth\, n.
   The quotient of a unit divided by eighty; one of eighty equal
   parts.