'tarnish-proof' originates from Modern English as a compound of the verb 'tarnish' and the suffix '-proof'. 'tarnish' ultimately comes from Middle English (from forms such as 'tarnishen'), and '-proof' comes from Old English/Old French sources related to 'proof' meaning 'tested' or 'resistant'.

'tarnish' developed in Middle English from earlier forms (e.g. 'tarnishen') meaning to make or become dull; 'proof' existed in Old English/Old French as a word meaning 'test' or 'resistant' and later became a productive suffix in Modern English to mean 'resistant to'. These elements were combined in Modern English to form the compound 'tarnish-proof'.

Initially, 'tarnish' referred to the action or process of becoming dull or discolored, and 'proof' referred to being tested; over time the compound 'tarnish-proof' came to mean 'resistant to tarnishing' as a single descriptive term.