'earnest' originates from Old English, specifically the word 'eornost', where the root meant 'seriousness, zeal'.

'earnest' changed from the Middle English word 'ernest' (from Old English 'eornost') and eventually became the modern English word 'earnest'.

Initially, it meant 'seriousness or zeal', but over time it evolved into its current adjectival sense of 'showing sincere and intense conviction' (i.e., 'serious' or 'sincere').