I get a yellow card (pay attention to the accents) for using "pàrtaidh" with an accent. Watson’s dictionary and AFB both use an accent as did all of the references I found in a short search of paper and internet resources with the exception of one: the mini dictionary at the back of Teach Yourself Gaelic (2010) which has “partaidh”. One dictionary which has its roots in MacAlpine (1831) does not contain a similar Gaelic word at all.
Most of the examples from AFB use the word in the sense of a political party or a faction as in a party in legal dispute/agreement. Indeed those Scottish political parties which have Gaelic language sites use Pàrtaidh in their titles. In all of this I encountered a rich seam of words and phrases used in Gaelic for various types of celebratory gatherings and indeed neither pàrtaidh nor partaidh appeared very much. So is this a case of either will do or is pàrtaidh/partaidh correct?