What is an antonym for contraption?

There isn't a single perfect antonym for "contraption" as the word carries a connotation of being complex, odd, or makeshift. However, depending on the context, some good options could be:

Simple: This emphasizes the opposite of being complex.

Device: This is a more neutral term for a tool or machine.

Mechanism: This implies a well-designed and functional system.

Appliance: This suggests a common and readily available tool.

Instrument: This emphasizes precision and purpose.

The best antonym would depend on the specific meaning of "contraption" in the context.