[Steve_Seattle]

"petros . . . petra"

My Greek is rusty, but I think your reply to CPA is correct. I do not think petros and petra are two different words (little stone vs. massive rock) in Greek, as CPA claimed, but the same word in a different case. Petros is used as a subject, whereas petra is the object of a preposition, and I think the word has a different ending depending how it is used in the sentence.

[eastsider]

The nominative and dative cases of petra do indeed have different endings (-a and -h, respectively); however, petros is masculine, and petra is feminine.