For example, in English, if there is more than one "boy", the word must become "boys." For example, "My family has two girls and one "boy", but my wife's family has two girls and three "boys"". The form "boy" is singular, meaning there is only one of the noun, and the form "boys" is plural, meaning there is more than one of the noun. You must know the noun's singular form if you want to find it in an English dictionary.