diner:
(plural: ‘diners‘; pronunciation: the letters ‘di’ rhyme with the word “die”)
a person who dines, usually at a restaurant, banquet, etc.,

a couple of diners enjoying their dinner (meal/food)
Mr Thomas is a regular diner at our restaurant.
This road side eatery serves late night diners who take a bite before going home after watching late night movies.
Most of the diners to the restaurant down the lane are from working class who like to have more quantity than quality of food for the price they pay.
Restaurants in this huge mall have fast foods served quickly for those diners who like to have a quick bite before going on their shopping spree!

an American diner (a roadside restaurant)
For an interesting article that explains what a diner is, please click here.
