Wiktionary (4.00 / 1 vote) Rate this definition: quay (Noun). A stone or concrete structure on navigable water used for loading and unloading vessels; a wharf. quay (Verb). To land or tie up at a quay or similar structure, especially used in the phrase quay up.Origin: From cai, from chai (modern French: quai).uay. A structure of solid construction along a shore or bank that provides berthing and generally provides cargo-handling facilities. A similar facility of open construction is called a wharf. See also wharf.