Diciottesima

Diciottesima is the feminine form of the Italian ordinal number diciottesimo, which designates the position after the seventeenth and before the nineteenth. It is used with feminine nouns to indicate order, for example: la diciottesima pagina (the eighteenth page), la diciottesima edizione (the eighteenth edition), la diciottesima volta (the eighteenth time). The form agrees in gender with the noun it accompanies, while the masculine form diciottesimo is used with masculine nouns (il diciottesimo capitolo, il diciottesimo giorno). Plural forms are diciottesime (feminine) and diciottesimi (masculine).

In fractional expressions, diciottesima is used with feminine nouns and diciottesimo with masculine ones. For instance, una diciottesima parte means one eighteenth part, while un diciottesimo di litro means one eighteenth of a liter.

Origin: the word is built from diciotto (eighteen) and the ordinal suffix -esimo, with the feminine ending -a.

Notes: the term is standard in Italian and appears in contexts such as literature, mathematics, and everyday language whenever a precise sequence or fraction is needed. When enumerating chapters, sections, or items, the appropriate gendered form must agree with the governing noun. See also Italian ordinal numbers and gender agreement in Italian.