cumpleaños
/kumpleˈaɲos/ · A2 · noun · m
birthday
🎂 cumple + años = completes + years: the day you complete another year
A compound of cumplir (to complete, fulfil; cousin of English accomplish) and años (years). Spanish says cumplir años for turning a year older, so a cumpleaños is literally a years-completing. Same form singular and plural: el cumpleaños.