IPA: /ˈtwɛntiəθ/
KK: /ˈtwɛntiəθ/
A part or position in a series that is number 20.
The twentieth chapter of the book was my favorite.
Twentieth → It is formed from "twenty" (from Old English "twentig", meaning two tens) and "-eth" (a suffix used to form ordinal numbers). The word "twentieth" means the ordinal form of twenty, indicating the position in a sequence as the two tens place.
Think of 'twenty' as two tens, and remember that 'twentieth' refers to the position of being in the sequence of twenty.
No commonly confused words.