'thirst-quencher' is a Modern English compound formed from the noun 'thirst' + the verb 'quench' with the agentive suffix '-er' (meaning 'one that or that which ...s'). 'thirst' comes from Old English 'þurst' and 'quench' comes from Old English 'cwencan'.

'thirst' changed from Old English 'þurst' to Middle English 'thurst/thurste' and became modern English 'thirst'; 'quench' changed from Old English 'cwencan' to Middle English 'quenchen' and then modern 'quench'. The compound 'thirst-quencher' arose in Modern English by combining these elements plus '-er'.

Originally the components referred separately to 'the sensation of needing drink' ('thirst') and 'to extinguish or put out' ('quench'); over time the compound came to mean specifically 'a thing (often a drink) that relieves thirst', a sense that is now standard.