1) Being one of 18 equal parts 2) Last golf hole 3) Next after the seventeenth 4) Ordinal 
• (a.) Consisting of one of eighteen equal parts or divisions of a thing. • (a.) Next in order after the seventeenth. • (n.) The eighth after the tenth. • (n.) The quotient of a unit divided by eighteen; one of eighteen equal parts or divisions.
Eight'eenth` adjective [ From Eighteen .] 1. Next in order after the seventeenth. 2. Consisting of one of eighteen equal parts or divisions of a thing. 
[adj] - coming next after the seventeenth in position 2. [n] - position 18 in a countable series of things
18th adjective coming next after the seventeenth in position
next after the seventeenth; being the ordinal number for 18. · being one of 18 equal parts.