'conscientious' originates from Latin, specifically the word 'conscientia,' where 'con-' meant 'with' and 'scientia' meant 'knowledge.'

'conscientia' transformed into the French word 'consciencieux,' and eventually became the modern English word 'conscientious' through Middle English.

Initially, it meant 'with knowledge or awareness,' but over time it evolved into its current meaning of 'careful and thorough.'