Πέτρος, Πέτρα (e.g., Matthew 16:18)

[bob144]

The name Christ gave Simon was Cehphas (in Aramaic) which became Greek Pevtroß Petras (which then became English Peter), because of the added s on the end of the Greek word it translates not to rock (which is pevtra petra) but to stone.
 In the verse Matthew 16:18 you can see the difference in the 2 words when looking at the original greek translation. The suggestion of femiinine masculine Peter Petra is not consisitent as the ending "as" on other male  names  Andreas (Andrew) is quite acceptable
Can anyone confirm this or add anything to this please? Particularly with the word petras being stone and petra meaning rock?
Thanks from Bob from Canada

[banned8]

There is extensive discussion of the matter on the web.

I don't think it would be responsible of me or anyone else to try to distinguish between two ancient Greek words, petros and petra, and on the basis of whatever difference there was in their meaning, and of whatever validity there is in Matthew 16:18, to create a dogma for papal supremacy. This is a matter for theologians, not for linguists.