? variant of STACK sb. 6.

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1775.  Ann. Reg., Chron., 185. The Abby,… having lately gone to pieces on the Stags near Kenrule, in Ireland, the captain, mate, and two common men … were cast upon the lower stags.

2

1867.  Smyth, Sailor’s Word-bk., Stag, a name given to a rock … as off the Lizard, Castlehaven, &c.

3