complejo
adjectiveCEFR B2
What does “complejo” mean in English?
complex — made up of many interacting parts; intrinsically multifaceted and difficult to reduce
complex — made up of many interacting parts; intrinsically multifaceted and difficult to reduce (una situación compleja, un sistema complejo)
Example sentences
La negociación del tratado es extremadamente compleja, ya que involucra intereses de más de veinte países.
Negotiating the treaty is extremely complex, as it involves the interests of more than twenty countries.
El diagnóstico reveló un cuadro clínico complejo con varias patologías que interactúan entre sí.
The diagnosis revealed a complex clinical picture with several interacting conditions.
Los algoritmos de inteligencia artificial son complejos por diseño, pero no siempre son complicados de utilizar.
Artificial intelligence algorithms are complex by design, but not always complicated to use.
How to use it
Complejo/a means 'complex' — made up of many interacting parts or elements, not easy to understand. It takes ser when describing an inherent quality. Key collocations: una situación compleja, un tema complejo, una red compleja de relaciones, el sistema es complejo. Critical distinction at B2: complejo (structurally intricate, many parts) vs complicado (hard to do or understand due to obstacles/tangling). A situation can be compleja (many interacting factors) without being complicada (unnecessarily difficult/troublesome).
Common mistake
Complejo and complicado are often confused. Complejo = intrinsically multi-layered (a complex system: many parts by design). Complicado = made difficult, unnecessarily tangled, or hard to execute (this is getting complicated). At B2, precision here matters: a complex (complejo) argument can be clear; a complicated (complicado) situation implies things have become messy. The worked example above shows the contrast explicitly.