The name is Ráithín, a diminutive of the Irish word ráth, meaning a ringfort, and the suffix itself carries a kind of affectionate diminishment, a little ráth, a small one.

A ráth or ringfort is an enclosed farmstead of the early medieval period, typically defined by one or more circular earthen banks and ditches, and used as a dwelling and farmyard between roughly the fifth and twelfth centuries. They are common enough across Ireland that hundreds survive in various states of preservation, yet many have vanished entirely from the ground while persisting in local memory and in place names. This one at Courtstown appears on the first edition Ordnance Survey six-inch map of 1839, which means surveyors working in that decade could still identify it as a distinct circular feature in the field. The local name Ráithín was recorded by O'Kelly in 1969, suggesting that even well into the twentieth century people in the area retained a name for it, passed down through ordinary use rather than scholarly preservation.