The words scalar, scaler sound the same but have different meanings and spellings. Why do scalar, scaler sound the same even though they are completely different words?
The answer is simple: scalar, scaler are homophones of the English language.
A quantity, such as mass, length, or speed, that is completely specified by its magnitude and has no direction.
Mathematics A number, numerical quantity, or element in a field.
A device that yields an output equal to the input multiplied by a constant, as in a linear amplifier.
Of or relating to a scalar.
An electronic circuit that records the aggregate of a specific number of signals that occur too rapidly to be recorded individually.
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").