Dictionary entry

ἀκρογωνιαῖος

G. Abbott-Smith's A Manual Greek Lexicon of the New Testament with Strong's

ἀκρο-γωνιαῖος, -αία, -αῖον

(< ἄκροι, γωνία, an angle) [in LXX: Is 28:16 (פִּנָּה)*;] = Attic γωνιαῖος (freq. in Inscr.; MM, VGT, s.v. ἀ.),

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