English definition of “one”
PARTICULAR PERSON/THING › used to refer to a particular person or thing in a group: One drawback is the cost of housing in the area. One of our daughters has just got married.
FUTURE TIME › used to refer to a time in the future which is not yet decided: We must have a drink together one evening.
TIME IN PAST › at a particular time in the past: I first met him one day in the park.
ONLY › only: He's the one person you can rely on in this place.
WITH ADJECTIVE mainly US › used to emphasize an adjective: That's one big ice cream you've got there!