noun, noun or participle which takes 'suru', intransitive verb
arriving first; first come, first served
Often used in the pattern 先着順 (first-come-first-served basis) or with する to mean 'arrive first'.
先着順で受け付けます。
We will accept applications on a first-come, first-served basis.
彼は会場に先着した。
He arrived at the venue first.
一番乗り is more colloquial and emphasizes being the very first person to arrive or do something, often with a sense of achievement. 先着 is neutral and commonly used in formal or procedural contexts.
Compound of 先 (before, ahead) and 着 (arrive). The meaning is transparent from its components.