What is the Gaelic word for kitchen?

There isn't one single Gaelic word for "kitchen". The term used depends on which Gaelic language you mean (Scottish Gaelic or Irish Gaelic) and even then, there might be regional variations.

* Scottish Gaelic: The most common word is cidsin, which is a borrowing from English. Older, less common terms might exist depending on the dialect.

* Irish Gaelic: The most common word is cóigcrios (although this can also mean "five-cornered room"). Again, regional variations or older terms might exist.

So, it's more accurate to say there's no direct equivalent and the word used is often a loanword from English.