Seven and Sevens

Seven noun - The cardinal number that is the sum of six and one.

Sevens is a synonym for seven. In some cases you can replace term "Sevens" with "Seven", this nouns are similar.

Sevens noun - A card game in which you play your sevens and other cards in sequence in the same suit as the sevens; you win if you are the first to use all your cards.

Seven is a synonym for sevens. You can use "Seven" instead a noun "Sevens".