STEP Greek Lexicon: ἀκρογωνιαῖος

ἀκρο-γωνιαῖος, -αία, -αῖον

(ἄκροι, γωνία, an angle) [in LXX: Isa.28:16 (פִּנָּה) * ;] = Attic γωνιαῖος (frequently in Inscr.; MM, VGT, see word ἀ.),

at the extreme angle: ὁ ἀ., the corner foundation stone, Eph.2:20, 1Pe.2:6.†

(AS)