What is the meaning of 'clusterbourach'?

The writer of this article is assuming the reader is familiar with a rather vulgar term, cluster fuck, given by M-W as:

a complex and utterly disordered and mismanaged situation : a muddled mess

I am not that familiar with the term bourach, but one of the meanings given in your own link is "mess." This could be connected to its other meaning of hovel, i.e. dwelling in a bad state of upkeep, but this is conjecture on my part.

So the writer has either made playful use of some rhetorical parallelism by adding the cluster in front of bourach for emphasis, or a slightly humorous attempt to bowdlerize his statement by replacing the vulgar portion of cluster fuck with something else. Whether the attempt worked and got the desired effect is another question.

The more common spelling of this is

clusterburach

meaning something like an 'awful great big complicated mess'. It has been used commonly recently to describe the legal difficulties in Brexit negotiations.

An example usage from recent news:

Scotland does deserve better. No reasonable person looking at the clusterburach at Westminster this week can deny that.”

It of course is patterned after the much more pejorative/taboo 'clusterfuck', a big mess. The interesting part is that

'burach' is Scots Gaelic for 'mess.

(thanks Spagirl for the dictionary link). So 'clusterburach' is two euphemism steps away from 'clusterfuck'.

_{Aside: there may be no trustworthy evidence for it but 'burach' may also mean 'duck', which may have been a multilingual rhyming euphemism (this is very questionable but entertaining). In other words, a cluster of ducks is not necessarily evocative of a terrible complication, but is associated by translation first and then by rhyming with a taboo word for 'a great big mess'. I have no evidence for this other than Google Translate, which is notoriously problematic for underrepresented languages like Gaelic in its various national forms, and idle, or rather motivated, speculation.}

You'll find the Scots term "bourach" in this online Scots dictionary. It's a loan word from Scottish Gaelic "bùrach", which means "a mess, a hash (of something)". The Scots loan takes on other meanings, but in the word clusterbourach it is simply a more emphatic way of calling something a "shambles" or a "mess". Can be spelled "bourach", "boorach", "burach".

http://www.scots-online.org/dictionary/scots_english.asp boorach [ˈbuːrəx, ˈbuːrɪç] n. A small mound, a heap of stones. A heap or mass. A crowd, a group, a cluster. A humble dwelling, a hovel, a mess. dim. boorachie, boorie NN.a. a small heap v. To heap up, mass profusely. To crowd together. bourach [ˈbuːrəx, NN.b. ˈbiːrəx] n. A band put round a cow's hinder legs at milking. v. To fetter.

Here is the Gaelic definition of bùrach. https://faclair.com/ bùrach /buːrəx/ fir. gin. ┐ iol. -aich 1 bourach, mess, guddle, shambles 2 (act of) delving, digging 3 jostling (in sports)

Bùrach is used in Dumfries to describe a large mess or F...Up! Some think it's local Dumfries "Scots", but it's Gàidhlig, it's Praiseach in Gaeilge. Watching Ian Blackford talking on Sky news live saying " Clusterbùrach" is the best TV I've seen this year!