Meaning

noun position 20 in a countable series of things

adjective coming next after the nineteenth in position

originFrom earlier twenteth, twentith, from Middle English twentithe, twentiþe, from Old English twēntigoþa. Equivalent to twenty + -eth. Etymological notes twentith, twenteth is the expected development from Middle English twentithe, but in time, the opaque twent- was replaced by a more transparent twenty-, resulting in modern twentieth (in the speech varieties this occurred in, the weak vowel in the…

Etymology from Wiktionary, CC BY-SA 3.0