"She has a silver fork."
Translation:Tá forc airgid aici.
'airgid' is the genitive case form of 'airgead'. The genitive case is mainly used for possession, but can also be used turning a noun into an adjective.
In the English phrase 'a silver fork', 'silver' is being used as an adjective meaning '(made) of silver'. To express this same meaning in Irish, we use the genitive case, thus we write 'forc airgid' to mean 'a silver fork', and it literally translates into English as 'a fork of silver'.