Dear PrueM
Patronymics set down a person's father, grandfather, great grandfather, and so on, rather like a pedigree. So you can be, for example, John Mackay, son of Angus, who was the son of Murdoch, who was the son of George. In Gaelic, "son" is written as "mac", and usually subsequent sons/grandsons etc as "mhic" pronounced "vic". If you are a woman, your line starts as "daughter of", but instead of "mac" you are "nic", or in Sutherland "nin".
Following this explanation, the patronymics in the Durness OPR can be worked out, provided we keep in mind that the minister who wrote them was a Gaelic learner, and wrote them out by their sound - that is, phonetically. In doing this, the minister, John Thomson, wrote in what now seems almost like a code, though in fact it follows the rules of Gaelic grammar. John (or Iain in Gaelic) is written often as "en", James (or Seumas) as "amish", George (which is Seoras) appears as "eoras", and so forth. "Mhic" appears as "ic".
So: "James Mackay alias Machustianmacnish" is James Mackay, the son of Hugh, son of Angus; and
"Donald Mackay alias Macneilmacenmacdholicuillam" is Donald Mackay, the son of Neil, son of John, son of Donald, son of William.
This is a wonderful help for genealogists, as it can reveal names back even five generations.
Margaret M