The words descendant, descendent sound the same but have different meanings and spellings. Why do descendant, descendent sound the same even though they are completely different words?
The answer is simple: descendant, descendent are homophones of the English language.
A person, animal, or plant whose descent can be traced to a particular individual or group.
Something derived from a prototype or earlier form: Today's bicycles are descendants of the earlier velocipede.
In astrology, the point of the ecliptic or the sign of the zodiac that sets in the west at the time of a person's birth or other event.
Variant of descendent.
Moving downward; descending.
Proceeding by descent from an ancestor.
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.