The words psalter, salter sound the same but have different meanings and spellings. Why do psalter, salter sound the same even though they are completely different words?
The answer is simple: psalter, salter are homophones of the English language.
The Book of Psalms. Often applied to a book containing the Psalms separately printed.
Specifically for Anglicans, the Book of Common Prayer which contains the Book of Psalms. For Catholics, the Breviary containing the Psalms arranged for each day of the week.
In the Roman Catholic Church, a rosary consisting of one hundred and fifty beads, corresponding to the number of the Psalms.
One that manufactures or sells salt.
One that treats meat, fish, or other foods with salt.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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.