'estimation' originates from Latin, specifically the word 'aestimatio' (aestimātiō), where the root 'aestimare' meant 'to value, to estimate.'

'estimation' passed into Old French as 'estimation' (from Latin 'aestimatio'), then into Middle English as 'estimacioun'/'estimatio(n)', eventually becoming the modern English 'estimation.'

Initially, it meant 'an act of valuing or assessing' and this core sense has remained, though it broadened to include 'opinion' or 'regard' as well as numerical estimates.