Lexical Definition

‎κυριακός‎ kyriakós (koo-ree-ak-os') the Lord’s ^G:A
from ‎κύριος‎

Lord's.

• belonging to the Lord (Jehovah or Jesus)

Abbott-Smith

**† κυριακός, -ή, -όν (< κύριος), [in LXX: κ. φωνή (Συριακή φ., R), II Mac 15:36 A*;]
1. as freq. in Inscr. (LS, s.v.; Deiss., BS, 217 f.), of the lord or master, imperial.
2. of the Lord (i.e. Christ): δεῖπνον, I Co 11:20; ἡμέρα, Re 1:10. (Cf. λόγια κ., Papias, Eus., HE, iii, 39, 1; γραφαὶ κ., Clem. Alex., etc; for eccl. usage, cf. Soph., Lex., s.v.)†

Abbott-Smith References

Liddell-Scott-Jones

κυριακός-ακός, ή, όν,

(κύριος) of or for an owner or master, [Refs 2nd c.AD+]; but usually of the Roman Emperor, ὁ κ. φίσκος the fiscus, [Refs]; κ. ψῆφοι, λόγος, [Refs 1st c.AD+]; κ. χρῆμα [Refs 2nd c.AD+]

__II especially belonging to the Lord (Christ): K. δεῖπνον the Lord's Supper, [NT]; ἡ K. ἡμέρα the Lord's day, [NT]; τὸ Κυριακόν (i.e. δῶμα) the Lord's house, Edict.Maximiniap.[Refs 4th c.AD+]
__III substantive κυριακός, ὁ, spirit invoked in magic, [Refs]

_{LSJ Scripture Refs: 1Cor.11.20}