a compound described in terms of the central atom to which other atoms are bound or coordinated
"In the lecture, Dr. Aris explained that the complex consists of a central iron atom coordinated to six cyanide ligands."
(psychoanalysis) a combination of emotions and impulses that have been rejected from awareness but still influence a person's behavior
"The therapist noted that his patient's recurring self-sabotage stemmed from an unresolved complex regarding his father."
a whole structure (as a building) made up of interconnected or related structures
"After years of expansion, the old factory has evolved into a complex of interconnected warehouses and offices that dominate the skyline."
A problem.
"The new software update introduced a complex bug that took hours to diagnose and fix."
In plain English: A complex is a group of buildings connected together, often surrounded by a wall or fence.
"The project was so complex that no single person could manage it alone."
Usage: Use "complex" as a noun to describe a situation involving many difficult or confusing factors that are hard to solve. It functions as a countable term, so you should say things like "a complex problem" rather than using it as an adjective for the difficulty itself.
To form a complex with another substance
"The iron ions quickly formed a colored complex with the cyanide solution when mixed together."
In plain English: To make something complicated by adding many different parts to it.
"The new software failed to properly complex the data from both servers."
Usage: Do not use "complex" as a verb in everyday conversation to mean making something complicated or difficult; that action is expressed by words like "complicate." The only time you should use "complex" as a verb is in scientific contexts where it specifically describes two substances chemically bonding together.
complicated in structure; consisting of interconnected parts
"a complex set of variations based on a simple folk melody"
"a complex mass of diverse laws and customs"
difficult to analyze or understand
"a complicated problem"
"complicated Middle East politics"
"he's more complex than he seems on the surface"
Made up of multiple parts; composite; not simple.
"The new engine is complex because it combines dozens of moving parts to generate power."
In plain English: Something complex is very complicated and hard to figure out because it has many confusing parts.
"The instructions for assembling the furniture were too complex to follow easily."
Usage: Use "complex" to describe something made of many interconnected parts that are difficult to understand or analyze. It applies to systems like machinery, ideas, or situations where the relationship between components creates a non-simple whole.
The word "complex" entered English from the French complexe, which comes from the Latin complexus. Originally meaning "entwined" or "encircled," it derives from roots that signify weaving things together.