/ˈɑːrmpɪt/
[noun] The hollow area under the shoulder where the arm joins the body. In informal use, it can also describe a place that is considered very unpleasant or dirty.
The word 'armpit' is surprisingly young — for most of English history, people called it the 'armhole', not the pit.
The word 'armpit' is a compound of two very ancient English words, each with its own long journey through history. The first part, 'arm', comes from Old English 'earm', which itself descends from Proto-Germanic 'armaz' and is related to the Proto-Indo-European root 'ar-', meaning 'to fit together' — the same root that eventually gave Latin its word 'armus', meaning 'shoulder joint'. This ancient root captures something precise: the arm is the limb that fits into the body at the shoulder. The connection runs deep across European languages, appearing in Old High German 'arm', Old Norse 'armr', and Gothic 'arms', all meaning the same thing.
The second part, 'pit', has an equally venerable history. It comes from Old English 'pytt', which was borrowed very early from Latin 'puteus', meaning 'a well' or 'a pit dug in the ground'. This Latin word is related to the verb 'putare', meaning 'to cleanse or prune', though the connection to a hole in the earth is the older and more dominant sense. The word 'pit' in English has always carried the idea of a hollow, a depression, or a cavity — whether in the ground or in the body.
Interestingly, the compound 'armpit' does not appear in written English until around the 16th century. Before that, English speakers used the term 'armhole' to describe the same part of the body — a word that sounds rather clinical to modern ears. The shift from 'armhole' to 'armpit' reflects a preference for the word 'pit' to describe bodily hollows, a usage that also survives in phrases like 'the pit of the stomach'. The older 'armhole' eventually retreated to a different meaning — the opening in a garment through which the arm passes — and it is still used in tailoring today.
The word gained a secondary, figurative meaning in 20th-century American English, where calling a town or place 'the armpit of somewhere' became a vivid way of saying it was the most unpleasant or undesirable part of a region. This usage plays on the armpit's reputation as a sweaty, unglamorous part of the body. Phrases like 'the armpit of the universe' appear in mid-20th century writing and speech, turning an ordinary anatomical term into a colourful insult for a location.
What makes 'armpit' quietly remarkable is how it reveals the way English builds words from simple, physical pieces. Unlike French 'aisselle' (from Latin 'axilla', meaning 'little axis' or 'little wing') or German 'Achselhöhle' (meaning 'axle hollow'), English chose a purely descriptive, almost blunt path: the pit that sits at the arm. There is no elegance of classical metaphor here, just practical observation — a hollow space beneath the arm — and that directness is very much in the spirit of Old English word-making.