'Nostra' originates from Latin, specifically the adjective 'noster, nostra, nostrum' meaning 'our' (the form 'nostra' is the feminine form).

'Noster/nostra' developed within Latin (from an earlier Proto-Italic form *noster) and was preserved into the Romance languages (e.g., Italian 'nostra') and into English mainly through fixed Latin or Italian phrases such as 'La Cosa Nostra' and titles like 'Nostra Aetate.'

Initially it meant simply 'our' (a possessive adjective in Latin); over time the form 'nostra' has been retained in set phrases and proper names in modern languages, where it can carry specialized or titular senses (for example, referring to the Mafia or to a specific council document).