Tráthnóna is a masculine noun that means evening.
In at least some areas of Munster, 'evening' is considered to begin about two or three hours after mid-day. This is reflected in both Irish and English. A statement such as tá an tráthnóna go hálainn or 'tis a fine evening would not be unusual to hear shortly after the dinner hour.
The language of Connacht and Ulster closer follows the English convention, with the morning (an mhaidin) being followed by the afternoon (an iarnóin) and the evening (an tráthnóna) starting some time after six.