I. (ˈ)ā(t)|tēn(t)th sometimes (ˈ)ād.|ē- adjective
Etymology: Middle English eightetenthe, eightenthe, adjective & noun, alteration (influenced by eightetene, eightene ) of eightetethe, eightethe, from Old English eahtatēotha, eahtēotha (akin to Old Norse āttjāndi, ātjāndi eighteenth), from eahtatīene, eahtatȳne, eahtatēne eighteen + -otha, -tha -th
1. : being number 18 in a countable series
the eighteenth day
— see number table
2. : being one of 18 equal parts into which something is divisible
an eighteenth share of the money
II. noun
( plural eighteenths -n(t)s, -n(t)ths)
Etymology: Middle English eightetenthe, eightenthe
1. : number 18 in a countable series
the eighteenth of the month
2. : the quotient of a unit divided by 18 : one of 18 equal parts of something
one eighteenth of the total