General:
* Submarine: A vessel that operates underwater.
* Suburb: A residential area located on the outskirts of a city.
* Subsequent: Occurring or coming after something else.
* Substitute: A person or thing that takes the place of another.
* Subject: A topic or theme.
* Subtle: Delicate or elusive.
* Submerge: To go underwater.
* Submit: To present something for consideration.
* Subsidy: Financial assistance given by a government.
* Subjective: Based on personal feelings or opinions.
Technical/Scientific:
* Subatomic: Relating to particles smaller than atoms.
* Subcutaneous: Located beneath the skin.
* Subdivision: A smaller part or division of something.
* Subspecies: A distinct variety of a species.
Other:
* Subpar: Below the expected standard.
* Subliminal: Below the level of conscious perception.
* Subtext: An underlying message or meaning.
* Subzero: Below zero degrees.
* Suboptimal: Not the best possible.
This is not an exhaustive list, but it provides a good starting point. You can use a dictionary or online resources to find more words starting with "sub".