'apr' (as the abbreviation 'APR') originates from modern English, formed from the initial letters of the phrase 'annual percentage rate'. 'Apr.' (abbreviation of 'April') originates from Latin, specifically the word 'Aprilis', where the root is associated with 'aperire' meaning 'to open'.

'apr' was created in modern English as an initialism of 'annual percentage rate' in technical/financial contexts. 'April' changed from Latin 'Aprilis' into Old English/Medieval forms such as 'Aprille' and eventually became the modern English word 'April'.

The abbreviation 'APR' developed as a modern technical shorthand for a financial rate; originally, the Latin root related to 'opening' (from 'aperire'), and over time that root became fixed as the name of the month 'April'.