Tooth (noun)

1. A hard bony structure in the mouth used for biting and chewing.
2. A projection on a gear or a saw used for engaging with another part.
3. A sharp projection on a tool used for cutting or scraping.

Origin:

Middle english, from old english tōth; akin to old high german zān tooth, latin dens, greek odous.

Examples:

1. She had a toothache and went to see the dentist.
2. The young boy lost his front tooth and was excited about getting money from the tooth fairy.
3. The gears were meshing smoothly because of their well-aligned teeth.
4. He used a saw with fine teeth to cut the wood.
5. The tool had several teeth that were used to scrape paint from the surface.