'atm' (as the cash-machine initialism) originates from English, specifically the words 'automated', 'teller' and 'machine' combined as the initialism 'ATM' in the mid-20th century; 'atm' (as the pressure abbreviation) originates from French/Latin via the English word 'atmosphere', ultimately from Greek roots.

'atm' as the abbreviation for 'automated teller machine' was formed in English in the 1960s from the initial letters of the phrase; 'atmosphere' comes from French 'atmosphère', from Latin scientific usage adapting Greek 'atmos' (vapor) + 'sphaira' (sphere), and was later abbreviated in scientific contexts to 'atm'.

The form 'atm' has been used for different modern technical abbreviations: initially (and older) as an abbreviation related to 'atmosphere' for pressure, and more recently also as the initialism for 'automated teller machine'; both senses coexist in modern usage.