1
: having parts that connect or go together in complicated ways
a complex system
The house's wiring is complex.
2
: not easy to understand or explain : not simple
a complex problem
The situation is more complex than you realize.
Her poetry is too complex [=complicated] for my taste.
3
grammar
: consisting of a main clause and one or more additional clauses
a complex sentence
plural complexes
1
: a group of buildings, apartments, etc., that are located near each other and used for a particular purpose
a sports complex
an industrial/apartment complex
2
: an emotional problem that causes someone to think or worry too much about something
She has a complex about her appearance.
3
: a group of things that are connected in complicated ways
a complex [=system] of welfare programs
a complex of protein molecules
Cite this Entry
“Complex.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/complex. Accessed 31 Oct. 2026.
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