/ˌkɒn.vəˈluː.ʃən/
[noun] A thing that is very complicated and difficult to follow, with many twisting or confusing parts. It can also refer to a coiled or twisted shape, like the folds of a brain or a rolled shell.
The convolutions of your brain are literally 'things rolled together' — your thoughts come from a word meaning a tight bundle of scrolls.
The word 'convolution' takes us back to classical Latin, where the key verb was 'volvere', meaning 'to roll' or 'to turn'. This was one of the most productive roots in all of Latin, carrying the core idea of rolling or revolving motion. From 'volvere', Latin built the compound verb 'convolvere' — using the prefix 'con-' (meaning 'together' or 'thoroughly') — to describe the act of rolling things together, winding one thing around another, or coiling tightly. The past participle of this verb was 'convolutus', meaning 'rolled together' or 'coiled up', and it is from this form that English directly drew the noun 'convolutio' (genitive: 'convolutionis') in its Late Latin shape.
The word entered English in the sixteenth century, initially carrying its most physical and literal meaning: a coiled, folded, or twisted shape. Scientists and anatomists of the period found it especially useful. When they looked at the human brain, they saw its characteristic ridges and furrows — tight, winding folds of grey matter — and 'convolution' became the precise technical term for each one of those folds. The brain's surface is still formally described as being full of convolutions, and the smooth brain of a foetus that has not yet developed them is called 'lissencephalic', from Greek for 'smooth brain', in direct contrast.
The Latin root 'volvere' was extraordinarily generative, and its influence on English is enormous. Through Latin 'volvere' → Old French 'volve' and related forms → Middle English, we get 'revolve'. Through Latin 'evolutio' → Old French 'evolution' → English, we get 'evolution' — literally an 'unrolling', as of a scroll. Through Latin 'involvere' → Old French 'involver' → English 'involve', we get the sense of being 'rolled into' something. Through Latin 'devolvere' → English 'devolve', we capture the idea of rolling something down or passing it on. Even the humble word 'volume' travels the same road: Latin 'volumen' (a rolled manuscript) → Old French 'volume' → English 'volume', preserving the ancient image of a rolled scroll as the basic unit of a book.
Over time, 'convolution' moved beyond the purely physical. By the seventeenth and eighteenth centuries, writers began using it figuratively to describe anything complex, tangled, or difficult to untangle mentally — an argument with too many twists, a plot full of unexpected turns, a bureaucratic process wound so tightly upon itself that no one could follow it. The shift makes perfect sense: if the physical image is of things wrapped around each other in layers, then a 'convoluted' explanation is one where the ideas are layered and twisted in just the same way, making it hard to find where one ends and another begins.
In the twentieth century, 'convolution' gained a fresh technical life in mathematics and signal processing, where it names a specific mathematical operation that blends two functions together by integrating one over the other — quite literally a process of 'rolling one function over another'. This use, now fundamental in digital image processing, artificial intelligence, and audio engineering, is a remarkable case of an ancient metaphor becoming a precise modern tool. The 'convolutional neural network', a cornerstone of modern machine learning, carries within its name the full weight of that Latin root: 'volvere', rolling forward through two thousand years of human thought.