The words senate, sennet, sennit sound the same but have different meanings and spellings. Why do senate, sennet, sennit sound the same even though they are completely different words?
The answer is simple: senate, sennet, sennit are homophones of the English language.
An assembly or a council of citizens having the highest deliberative and legislative functions in a government, specifically:
The upper house of the U.S. Congress, to which two members are elected from each state by popular vote for a six-year term.
The upper house in the bicameral legislature of many states in the United States.
The upper legislative house in Canada, France, and some other countries.
A call on a trumpet or cornet signaling the ceremonial exits and entrances of actors in Elizabethan drama.
Any of several barracudas, especially Sphyraena borealis, of the western Atlantic.
Braided cordage formed by plaiting several strands of rope fiber or similar material.
Plaited straw, grass, or palm leaves for making hats.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").