What is another word for complex?

The best substitute for "complex" depends on the context. Here are some options:

For something intricate or complicated:

* Intricate

* Elaborate

* Sophisticated

* Multifaceted

* Multilayered

* Detailed

* Complicated

* Convoluted

* Tangled

* Difficult

* Challenging

For something with multiple parts:

* Composite

* Compound

* Combined

* Integrated

* Multi-component

* Structured

* Organized

For something with a hidden meaning:

* Symbolic

* Allusive

* Subtle

* Ambiguous

* Mystifying

* Mysterious

For something that is difficult to understand:

* Abstruse

* Arcane

* Cryptic

* Esoteric

* Inscrutable

* Obscure

For a building:

* Building

* Structure

* Facility

* Installation

For a group of buildings:

* Development

* Estate

* Compound

For a feeling or idea:

* Complicated

* Confusing

* Troublesome

* Difficult

* Mixed

* Ambivalent

* Conflicted

To choose the best word, consider the specific meaning of "complex" in your sentence and the tone you want to convey.