The Proto-Indo-European word *posti
Word *posti
Meaning after
See also Proto-Indo-European: *pos ‘behind, immediately adjacent, following’

Comments
Mallory J.P. and Adams D. (2006)

Other words that might be of interest
*wet- ‘year’, *h₁en- ‘year’, *kēs(k̂)ehₐ ‘time’, *kʷóm ‘when’, *kʷodéhₐ ‘when’, *sem- ‘at one time, once’, *(h₁)yēro/ehₐ ‘year, new season’, *hₐetnos ‘year’, *wételos ‘yearling’