It is a souterrain, a type of subterranean structure built during the early medieval period in Ireland, typically consisting of one or more dry-stone chambers connected by narrow crawlways. Their precise purposes are still debated, though most scholars associate them with food storage, refuge, or both. That one exists at Tiraninny is known; what it looks like, how large it is, and what condition it survives in are details not yet available in the public record.

Souterrains are found across Ireland in considerable numbers, often associated with ringforts or early ecclesiastical settlements, and Mayo has its share. They tend to be discovered by accident, through agricultural work or ground subsidence, and are frequently only partially excavated. The townland name Tiraninny likely derives from the Irish, though without further detail about the local landscape or any associated monuments nearby, the specific story of this particular example remains elusive. It is, in the formal sense, a placeholder in the archaeological record, acknowledged but not yet fully described.