A translation of the bible in Spanish (La Biblia Textual – 3ra Edición) translates:
κυριακὸν δεῖπνον = cena dominical (dominical supper) — 1 Corinthians 11:20
κυριακῇ ἡμέρᾳ = día dominical (dominical day) — Revelation 1:10
A marginal note says that these words must be translated as an adjective instead of indicating belonging.
Nevertheless, most of the translations translate these verses as “Lord’s supper” and “Lord’s day”, respectively. Although the Lord’s day is traditionally identified as Sunday, did Paul have in mind the day Sunday on 1 Corinthians 11:20? Is it plausible to translate κυριακὸν and κυριακῇ as an adjective (dominical) instead of indicating belonging?