| Term | Definition |
| sub | under, below |
| subconscious (adj) | not fully aware; occurring below your level of thinking and awareness |
| subcutaneous (adj) | under the skin |
| subdue (v) | to bring under control |
| subfreezing (adj) | below the freezing point |
| subirrigate (v) | to water something from under the ground |
| subject (v) | to put under someone else's control |
| submarine (n) | a watercraft that stays under water |
| submerge (v) | to put under water |
| subordinate (n) | a person who is under someone else in rank or importance |
| subway (n) | a passageway under the ground; an electric underground railway |