E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Clear out for Guam (To).
The ship is bound for no specific place. In the height of the gold fever, ships were chartered to carry passengers to Australia without having return cargoes secured for them. They were, therefore, obliged to leave Melbourne in ballast, and to sail in search of homeward freights. The Custom House regulations required, however, that, on clearing outwards, some port should be named; and it became the habit of captains to name Guam (a small island of the Ladrone group) as the hypothetical destination. Hence, to clear out for Guam came to mean, clear out for just anywherewe are bound for whatever coast we may choose to venture upon. (See Notes and Queries, April 18th, 1885, p. 314.)