Thanks for the great Tim Staples link--very informative stuff. In my Liddell-Scott Greek Lexicon it does indeed say "petros, a stone, distinguished from petra [a rock]". But I notice that the two quoted passages are Homer, which is very early Greek, and Euripides which is what...classic Attic? It seems likely to this armchair amateur that in the koine Greek of the NT such distinction could well have been obliterated--and apparently these two actual scholars are saying that flat out.
"It seems likely to this armchair amateur that in the koine Greek of the NT such distinction could well have been obliterated--and apparently these two actual scholars are saying that flat out."
Yes, and there is also the question of the puns: the one Jesus made in Aramaic, which the writer of the Greek tried to preserve in that language.
Now when the the gospel of Matthew was written in Greek, either by the author himself, or by a later translator (in fact, there is much evidence from the early church to support an Aramaic original; Papias, Irenaeus, Origen, Eusebius, Chrysotom, Epiphanius, Augustine), an effort was made to preserve the pun so apparent in the Aramaic language. There was one problem though that the Aramaic language didn't have, as well as other languages such as English and French. In Aramaic, the verse would read: You are Kepha and upon this kepha. Greek nouns have gender specific endings though. So in verse 18, when the writer needed to replace each 'kepha' with a Greek equivalent, he ran into a problem. The word 'petra' could be used for the second appearance of kepha in the verse, but because 'petra' is feminine in gender, it couldn't be used for a man's name. In order to do this, a masculine ending had to be placed on it, and this is where 'petros' comes about. As I said before, many languages don't have this problem as can be seen by a rendering of this verse in each language:
French: Tu es Pierre et sur cette pierre
Old Syriac: Anath-her Kipha, v'all hode kipha
http://www.geocities.com/orthopapism/kipha.html