* Comunn: This translates more to "gathering" or "meeting" and could work for a social gathering.
* Fèis: This refers to a festival or celebration, suitable for a larger, more formal event.
* Ceilidh (pronounced kay-lee): This is probably the closest single word. It refers specifically to a traditional Scottish social gathering with music and dancing. While not *every* party is a ceilidh, it's often the word used informally for a lively party.
Therefore, the best word to use depends heavily on the context.