English
posteriorly
From posterior + -ly.
A compound of posterior + -ly
Proto-Indo-European *pós ‘afterwards, post-’
…
Proto-Italic *posti ‘behind, after’
Proto-Italic *posteros ‘later’
Latin posterus ‘following, next, coming after’
Latin posterior ‘that comes or follows after’
English posterior
Today it means
adv After (in time).
Language periods are conventional ranges, not dates for this word.
Etymograph / posteriorly