Steillthún

This is compound placename for the actual point on the west side of the Shrón probably comes from steill=steall=splash with thún being a variation of thonn (wave)

Steillthún is a coastal rock feature likely composed of basalt, formed by ancient volcanic activity and subsequent erosion by wave action. Its name reflects its notable exposure to wave splash, indicating its position at a dynamic and possibly prominent coastal point.