πέτρα, -ας, ἡ,
[in LXX chiefly for סֶלַע, צוּר;]
a rock, i.e. a mass of live rock as distinct from πέτρος, a detached stone or boulder: Mt 7:24, 2527:51, 60, Mk 15:46, Lk 6:488:6, 13; of a hollow rock, a cave, Re 6:15, 16 (cf. Is 2:10, al.). Metaph., Mt 16:18 (on the meaning, v. Hort, Eccl., 16 ff., but cf. also ICC, in l.), I Co 10:4; = πέτρος, Ro 9:33, I Pe 2:8(LXX).†