'ardency' originates from Old French/Middle English, ultimately from Latin 'ardēns' (present participle of 'ardēre'), where the Latin root 'ardēre' meant 'to burn'.

'ardency' changed from Middle English 'ardence' (from Old French 'ardence'/'ardent') and eventually became the modern English word 'ardency'.

Initially it was associated with 'burning' or 'heat' (literal sense from Latin), but over time it evolved into the figurative sense of 'intense feeling' or 'passion'.