'axilla' originates from Latin, specifically the word 'axilla' (a diminutive of 'axis'), where 'axis' meant 'axle' or 'pivot' and the diminutive conveyed 'little axis' used anatomically for the hollow under the arm.

'axilla' was used in Classical Latin, passed into Late Latin/Medieval Latin with the same form, and was later borrowed into English (medical/technical use) as 'axilla' with plurals 'axillae' or anglicized 'axillas'.

Initially linked to the idea of a 'small axis' (diminutive of 'axis'), it came to be used anatomically for the underarm hollow; the modern meaning is specifically 'armpit' or 'underarm area'.