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 : Mat.7:24-25 27:51, 60 Mrk.15:46, Luk.6:48 8:6, 13; of a hollow rock, a cave, Rev.6:15-16 (of. Isa.2:10, al.). Metaphorical, Mat.16:18 (on the meaning, see Hort, Eccl., 16 ff., but cf. also ICC, in l), 1Co.10:4; = πέτρος, Rom.9:33, 1Pe.2:8" (LXX) .†
(AS)