As nouns the difference between quay and kay

is that quay is a stone or concrete structure on navigable water used for loading and unloading vessels; a wharf while kay is a kilometer.

As a verb quay

is to land or tie up at a quay or similar structure, especially used in the phrase "quay up".

As an interjection kay is

abbreviation of lang=en.

As a proper noun Kay is

{{surname|from=Middle English}} derived from several Old and Middle English words; also adopted by immigrants whose surnames began with a K.