The words censer, censor, senser, sensor sound the same but have different meanings and spellings. Why do censer, censor, senser, sensor sound the same even though they are completely different words?
The answer is simple: censer, censor, senser, sensor are homophones of the English language.
A vessel in which incense is burned, especially during religious services.
A person authorized to examine books, films, or other material and to remove or suppress what is considered morally, politically, or otherwise objectionable.
An official, as in the armed forces, who examines personal mail and official dispatches to remove information considered secret or a risk to security.
One that condemns or censures.
One of two officials in ancient Rome responsible for taking the public census and supervising public behavior and morals.
An obsolete spelling of censer.
A device, such as a photoelectric cell, that receives and responds to a signal or stimulus.
See sense organ.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from The Century Dictionary and Cyclopedia 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").