retroactive
'influencing or applying to a period prior to enactment, directed backwards in time’
Lexical development traced from the Tamil root:
E. retroactiue < F. rétroactif ‘casting or relating back’ < Lat. retroact- < retroagere ‘drive or turn back’ < retro ‘back’ + agere ‘to drive, set in motion’ < ak < ag- < Tamil ukai