"A hundred thousand welcomes, sister!"
Translation:Ceud mìle fàilte a phiuthar!
For "a hundred thousand welcomes, sister" I put Ceud mìle fàilte, a phuithair but it was marked wrong and should have been Ceud mìle fàilte, a phuithar a) I feel a bit cheated because I was only 1 letter out and b) I genuinely thought it needed the extra i as it was the vocative. What am I not understanding? (Especially when you hover over the word sister and a Phuithair comes up...)
You are right, but this problem has history on this site. Phiuthar (note the spelling, as pointed out by Jevon381231) is probably the only feminine word ending in -ar you will ever meet that you would want to put in the vocative, which is why people often get this one wrong. In particular, it was originally wrong on this site, which could mean that AmandaFlee1, who was writing over a year ago, could have just seen the wrong form. See discussion here.
The rule is commonly quoted the way you have but this frequently leads to confusion when people try to apply the rule to masculine plural nouns. So, just to clarify,
you add the 'i' when it's masculine singular
If you are interested in the historical reason for this i-insertion here, see my answer here.
Halò! When I mouse over "sister," the hints are "phiuthar" and "a phiuthair," but when I answered "a phiuthair" it was marked as a typo. (The correct answer being "a phiuthar," without the second 'i.') Is there a typo in the answer/hints here, or am I misunderstanding something?
Tapadh leibh! :)
The confusion is caused by the majority of Gaelic words (i.e. the masculine ones) adding the i in the vocative. Piuthar is, needless to say, feminine, and so this rule is not applied.
If you go back into the mists of time, this inserted i would have been an i or e in the ending. So if you know Latin you can compare domine (masc) with domina (fem).
To add to the confusion, vocatives is -ar are vanishingly rare. First, some word for family members also end in an -r but they already have an i in = màthair and athair, Then feminine words more commonly end in a slender consonant than masculine ones. So I did not expect to find many. A search of Dwelly revealed only a handful. None was likely to be used in the vocative, and some were obsolete, obscure or dialectal. I found ones meaning 'full sea', 'east', 'goat', 'vinegar', 'difference', 'deafness', 'drove', 'afterbirth' and 'goal'. So none with much chance of occurring in the vocative. I suppose you might want to talk to a goat, but for all practical purposes, piuthar is the only vocative in all of Gaelic that ends -ar, although there are quite a lot, including common ones, that end in -air. So definitely an easy mistake to make.