English definition of “first”
A1 before everything or everyone else: Jason came in first in the race (= he won).
B1 for the first time: I first met him last year.
at first B1 at the beginning of a situation or period of time: I didn’t like her at first, but now we are friends.
first; first of all B1 before doing anything else: First of all, make sure you have all the ingredients.