'punctilious' originates from Italian, specifically the word 'puntiglio', ultimately reflecting Latin 'punctum' where 'punct-' meant 'point'.

'punctilious' changed from earlier English use of 'punctilio' (meaning 'a fine point or petty nicety') and later formed the adjective 'punctilious' in modern English; the adverb 'punctiliously' is derived from that adjective.

Initially, it meant 'concern with small points (especially of etiquette or ceremony)', but over time it evolved into its current meaning of 'showing meticulous attention to detail and correctness'.