That uncertainty is itself quietly telling. Ireland's landscape is scattered with earthworks of many kinds, from the enclosing banks of ringforts to the low ridges of field systems abandoned during the Famine, and the term covers a broad range of human-made or human-modified ground features. Without further detail, Feenish holds its particular earthwork close.

Feenish sits in the waters of the Shannon Estuary, one of several small islands in that stretch of County Clare coastline. Islands of this kind often carry traces of early medieval activity, sometimes monastic, sometimes agricultural, sometimes defensive, left by communities for whom the water offered protection as much as isolation. An earthwork in such a setting might mark an enclosure, a boundary, or the remains of a structure long since robbed of its stone. What it represents specifically on Feenish is a question that currently has no published answer.