'armpit' originates from Old English, specifically the compound 'earmpytt', where 'earm' meant 'arm' and 'pytt' meant 'pit' or 'hollow'.

'armpit' changed from Old English 'earmpytt' (and related Middle English forms such as 'armputte'/'armpitte') and eventually became the modern English word 'armpit'.

Initially, it meant 'a hollow under the arm'; this primary anatomical meaning has been retained, though the word also developed a figurative slang sense meaning 'a very unpleasant place'.