A strong current or furious tide betwixt island groups.
“This lofty promontory is constantly exposed to the current of a
strong and furious tide, which, setting in betwixt the Orkney and
Zetland islands, and running with force only inferior to that of the
Pentland Frith, ... is called the Roost of Samburgh [from the
Gone to roost. Gone to bed. (Anglo-Saxon, hrost.)
“The chough and crow to roost are gone.”
Glce (words by Joanna Baillie, music by Bishop).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894