A roll or knot of hair. A common hairstyle for Roman and Greek women in the first century was long hair parted in the middle and wound into a knot in the back of the head. See a sculpture of a Roman woman showing this hairstyle.
A chignon is a sophisticated, elegant up style, where long hair is twisted (either in a roll or knot) and pinned from the nape of neck. This style is synonymous with the Hollywood and the Oscars, without a single strand of hair out of place.
A chignon is a type of bun hairstyle, made popular and worn by many women. A chignon looks like a doughnut with a tiny hole in the middle with hairpins that are concealed.