a sharp pointed object driven into flesh, anywhere from a thorn or splinter to a heavy impaling stake
This word names something sharp that pierces the body, but how big and how violent it is shifts with the writer. In the older epic and high literary Greek it meant a stake: a sharpened pole set in a defensive ditch, or the pale on which a body was impaled. In the everyday Greek of letters, medical writers, and the Greek Old Testament it had narrowed to a thorn or a splinter, a small foreign body lodged in skin or eye. So the one word can carry a whole range, from a needle a doctor uses to pull out a sliver, to the spike a victim is hung on.
The word appears only once in the New Testament, in Paul's "thorn in the flesh" (2 Corinthians 12:7), and that single use is famous precisely because the range matters. Read it as a thorn or splinter and the affliction sounds chronic and humiliating but bearable. Read it as a stake and the image turns violent, a man pinned and helpless. The Greek Old Testament, which is the Greek Paul read and quoted, always uses the word for a thorn or brier, and always as a picture of something God allows to prick and harass his people, sometimes a painful ailment, sometimes hostile neighbors. That is the background most scholars think Paul drew on.
The heavier sense was still alive in Paul's day. Writers attacking the early Christians used this very word, and its related verb, to sneer at the cross as a thing of impalement. Some readers think Paul knew both registers and let the word carry both at once: a thorn to ears tuned to the Greek Old Testament, a stake to ears tuned to the older epics.