In Koiné Greek, all nouns contain case, gender, and number. By case, a noun can be nominative, genitive, dative, accusative, or vocative. By number, a noun can be singular or plural. By gender, a noun can be masculine, feminine, or neuter. Nouns are listed in a Greek dictionary by their nominative masculine singular form.
Sometimes the actual classification of a noun does not match its form. For example, a noun can appear dual when it is actually plural; a noun can appear masculine when it is actually feminine; and so on.