Rock - Vine's Expository Dictionary of New Testament Words
Rock[ 1,,G4073, petra ]
denotes a mass of rock," as distinct from petros, "a detached stone or boulder," or a stone that might be thrown or easily moved. For the nature of petra, See Matthew 7:24-Matthew 7:25; Matthew 27:51, Matthew 27:60; Mark 15:46; Luke 6:48 (twice), a type of a sure foundation (here the true reading is as in the RV, "because it had been well builded"); Revelation 6:15-Revelation 6:16 (cp. Isaiah 2:19,ff.; Hosea 10:8); Luke 8:6, Luke 8:13, used illustratively; 1 Corinthians 10:4 (twice), figuratively, of Christ; in Romans 9:33; 1 Peter 2:8, metaphorically, of Christ; in Matthew 16:18, metaphorically, of Christ and the testimony concerning Him; here the distinction between petra, concerning the Lord Himself, and Petros, the Apostle, is clear (See above).
[ 2,,G4694, spilas ]
"a rock or reef," over which the sea dashes, is used in Jude 1:12, "hidden rocks," RV, metaphorical of men whose conduct is a danger to others. A late meaning ascribed to it is that of "spots," (AV), but that rendering seems to have been influenced by the parallel passage in 2 Peter 2:13, where spiloi, "spots," occurs.