IPA: /ˈsɪksθli/
KK: /sɪksθli/
In the sixth position or order; used to indicate the sixth item in a list or sequence.
The committee discussed the proposal sixthly, after addressing the first five points.
Sixthly → It is formed from "sixth" (from Old English "sixta", meaning the ordinal number after fifth) and the suffix "-ly" (meaning in a manner of). The word "sixthly" means in the manner of the sixth item or point.
Think of the word 'sixth' to remember that 'sixthly' refers to something done in the manner of the sixth item.
No commonly confused words.