I encountered a new term this week: the word "clachan."

I found it while reading Out of Ireland: The Story of Irish Emigration to America by Kerby Miller and Paul Wagner (Elliott & Clark Pubishing, 1994). Writing about overpopulation and famine, the authors described how the 19th century Irish countryside was filled with people:

"Many Catholic peasants lived in crowded rural settlements called clachans. A few dozen, or even several hundred, one- or two-room thatched cottages were clustered together, surrounded by unfenced fields for raising potatoes and a few stunted livestock..."

Here's part of an illuminating definition of "clachan" at Encyclopedia.com:

"The house cluster, consisting of irregular groupings of farmhouses often in association with an unenclosed and communally worked field system, was found extensively in the western regions of Ireland in the nineteenth century. This settlement form contrasted with the dispersed single farmstead, which is most characteristic of the Irish landscape in modern times. The geographer Estyn Evans christened these clusters clachans (a term with no known provenance in Irish linguistic tradition) on the basis of a similarity with a Scottish settlement of this name..." 

If you're interested in learning more about the (apparently somewhat controversial) historical concept, here's a link to the Encyclopedia article.