'expectorant' originates from Latin, specifically the word 'expectorare', where 'ex-' meant 'out' and 'pectus' meant 'chest'.

'expectorant' changed from the Late Latin present participle 'expectorans' (from 'expectorare') and was adopted into English via medical/Latin usage as 'expectorant'.

Initially it meant 'to remove (something) from the chest' (literally 'to clear the chest'), but over time it evolved into its current meaning of 'a substance or agent that promotes the discharge of phlegm'.