The words pica, pika sound the same but have different meanings and spellings. Why do pica, pika sound the same even though they are completely different words?
The answer is simple: pica, pika are homophones of the English language.
A printer's unit of type size, equal to 12 points or about 1/6 of an inch.
An equivalent unit of composition measurement used in determining the dimensions of lines, illustrations, or printed pages.
A type size for typewriters, providing ten characters to the inch.
An abnormal craving or appetite for nonfood substances, such as dirt, paint, or clay.
Any of several small, tailless, furry mammals of the genus Ochotona of the mountains of North America and Eurasia, resembling guinea pigs but belonging to the order of lagomorphs that includes the hares and rabbits. Also called coney1, rock rabbit.
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").