1.
postdating; advance dating
Writing a future date on a document, check, or other item, so that it becomes effective at that later date.
2.
appetizer; first course (in kaiseki cuisine)
The opening dish served at the beginning of a kaiseki or traditional Japanese multi-course meal, typically a small, seasonal appetizer.
Two distinct meanings sharing the same word.
SENSE 1 (postdating): Formed from 先 (ahead/future) and 付ける (to attach/put). Refers to marking a document with a date in the future. Common in business and financial contexts.
SENSE 2 (kaiseki appetizer): In 懐石料理 (kaiseki cuisine), the 先付け is the opening course, served before everything else. It sets the tone and showcases the season's flavors. The name literally means "served first." This sense is also written as 先附け.