/ˈkɒmpleks/
[adjective] Made up of many connected parts that are difficult to understand or deal with. Something complex has many pieces that work together in ways that are not always easy to see or explain.
The word 'complex' literally means 'woven together' — every complicated thing in your life is, at its root, a piece of fabric.
The story of 'complex' begins in ancient Rome, with a Latin verb of remarkable physical simplicity: *plectere*, meaning 'to weave' or 'to braid'. This was the same root that gave Roman soldiers the word for a woven fence or a plaited basket — something made of many strands intertwined into one structure. The prefix *com-*, meaning 'together' or 'with', was added to produce *complectere*, meaning 'to embrace', 'to encircle', or 'to entwine'. From this verb came the past participle *complexus*, describing something that had been braided or woven together into a unified whole.
The Latin adjective *complexus* evolved into the noun and adjective *complexus* and later *complexum*, used by Roman writers to describe things made of many interrelated parts — a kind of intellectual weaving, where ideas or elements were understood not in isolation but in their relationships to each other. The great Roman orator Cicero used related forms when speaking about the connections between arguments in a speech, treating logic itself as a kind of weaving. This metaphorical leap — from physical braiding to intellectual entanglement — was the crucial step that gave 'complex' its modern life.
The word passed from Classical Latin into Medieval Latin, where scholars used *complexio* to describe the combination of qualities that made up a person's character or constitution. This Medieval Latin *complexio* then moved into Old French as *complexion*, and from Old French into Middle English as *complexion* — a word that originally meant a person's overall physical and emotional nature, not just the colour of their skin. That narrowing of meaning happened gradually in English, and it is why today 'complexion' refers only to the face, even though its ancestor once described the whole weave of a human personality.
The adjective 'complex' itself arrived in English in the mid-17th century, borrowed directly from the Latin *complexus*. Early English writers used it in mathematics and philosophy to describe numbers or ideas made up of more than one part. The word quickly spread beyond technical language, and by the 18th century it was used freely to describe anything with many interlocking elements. Alongside it came the noun 'complex', which in the 20th century gained a powerful new meaning in psychology: Sigmund Freud and Carl Jung used it to describe a cluster of emotions and memories woven together in the unconscious mind — an 'inferiority complex' or an 'Oedipus complex' being, quite literally, a tangle of feelings from which a person cannot easily escape.
The Latin root *plectere* has been remarkably generous to English, producing a whole family of words through different prefixes. *Com-* + *plectere* gave us 'complex' and 'complexion'. *Im-* + *plectere* → Latin *implicare* → Old French *implier* → English 'imply'. *Ex-* + *plicare* (a related weaving verb) → Latin *explicare* → French *expliquer* → English 'explain'. *Per-* + *plexus* gave us 'perplexed', meaning so thoroughly entangled that you cannot find your way out. Even 'perplex', 'duplex', and 'multiplex' carry the old image of braided threads. When you call something complicated, you are reaching all the way back to a Roman craftsman folding strands over one another — and finding, perhaps, that language itself is the most complex weaving of all.