Quick Definition
ἀκρογωνιαῖος, α, ον Adj in the corner, cornerstone
Strong's Definition
from 206 and 1137; belonging to the extreme corner
KJV Usage: chief corner
UBS Dictionary of the Greek New Testament
adjc. | -α, -ον | ἄκρον + γωνία
7.44 · Constructions · Parts and Areas of Buildings
cornerstone, important stone the cornerstone or capstone of a building, essential to its construction (this term occurs in the NT only figuratively in reference to Christ) Some scholars have assumed that ἀκρογωνιαῖος would refer to the capstone occurring at the high point of a peaked roof, but in the NT ἀκρογωνιαῖος would probably refer to the type of stone which would have been used in the Temple in Jerusalem, and therefore it is far more likely to understand ἀκρογωνιαῖος as a cornerstone rather than a capstone of a peaked roof. It would not have referred to the keystone of an arch. Since, however, in many societies the use of ‘cornerstone’ is not known and in others it may have an entirely different function, it may be more satisfactory to use an expression such as ‘the most important stone’ or ‘the very important stone.’ This serves to describe the function and significance of the cornerstone without trying to indicate precisely its location or form.
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Mounce Concise Greek Dictionary
ἀκρογωνιαῖος akrogōniaios 2x
literally: lying at the extreme corner; with λίθος, corner or foundation stone, Eph. 2:20; 1 Pet. 2:6*
Abbott-Smith Greek Lexicon
† 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.†
Moulton & Milligan — Vocabulary of the Greek NT
ἀκρογωνιαῖος may very well have been coined by the LXX (Isa 2818). The Attic word was γωνιαῖος : see inscriptional citations in J. A. Robinson Aphesians, p. 164. Cronert (p. several other compounds of ἄκρος, some of which may be in the same category. W. W. Lloyd in CA iii. p. 419a (1889) among some architectural notes on Eph 259-59, says: ‘* The acrogoniaios here is the primary foundation-stone at the angle of the structure by which the architect fixes a standard for the bearings of the walls and cross-walls throughout.” 233) has
Liddell-Scott-Jones — Greek-English Lexicon
ἀκρογωνιαῖος (akrogōniaios) — cornerstone. ἀκρο-γωνιαῖος, α, ον, at the extreme angle, ἀ. λίθος corner foundation-stone, [LXX+NT]