Stac an Armin, based on the proper Scottish Gaelic spelling, is a sea stack in the St Kilda archipelago. It is 196 metres (643 ft.) tall, qualifying it as a Marilyn. It is the highest sea stack in Scotland and the British Isles.

St Kilda is a remote archipelago situated 64 kilometres (40 mi) west-northwest of North Uist in the North Atlantic Ocean. It contains the westernmost islands of the Outer Hebrides of Scotland. The largest island is Hirta, whose sea cliffs are the highest in the United Kingdom; three other islands were also used for grazing and seabird hunting. The islands are administratively a part of the Comhairle nan Eilean Siar local authority area.