General:
* Spectacle: A public display or performance.
* Spectacular: Impressive or grand in appearance or scale.
* Speculate: To form opinions or theories without having definite knowledge.
* Speculative: Based on guesswork or conjecture.
* Specter: A ghost or phantom.
Scientific:
* Species: A group of organisms that can interbreed and produce fertile offspring.
* Specific: Clearly defined or particular.
* Specimen: A single example of something, typically used for scientific study.
* Spectroscope: An instrument used to analyze light.
* Spectrum: A band of colors or wavelengths.
Other:
* Inspect: To look at something carefully in order to check its condition.
* Prospect: The possibility of something good happening.
* Respect: Esteem or admiration for someone or something.
* Suspect: To believe that someone is guilty of a crime.
* Expect: To think or believe that something will happen.
This is not an exhaustive list, as there are many more words that use the root "spec" in different combinations.