"Welcome and good afternoon."
Translation:Fàilte agus feasgar math.
Afternoon and evening are both masculine. Morning is feminine, night is feminine.
I'm not sure why feasgar is the odd one out but it probably has something to do with the Latin origins of those words (they went from Latin to Old Irish and then the modern languages).
Feasgar comes from vesper which is an evening meal. Madainn comes from Mātutīnus which means "of the morning" (from the goddess Mātūta) Oidhche possibly comes from the latin āter, which means "dark".