Lexical Definition

‎ἀκρογωνιαῖος‎ akrogōniaîos (ak-rog-o-nee-ah'-yos) cornerstone ^G:A
from ‎ἄκρον‎ and ‎γωνία‎

chief corner.

• belonging to the extreme corner

Abbott-Smith

† 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.†

Abbott-Smith References

Liddell-Scott-Jones

ἀκρογωνιαῖος-γωνιαῖος, α, ον,

at the extreme angle, ἀ. λίθος corner foundation-stone, [LXX+NT]

_{LSJ Scripture Refs: LXX.Isa.28.16 ☩ Eph.2.20}