Definition of "argal"

And an act hath three branches—it is to act, to do, to perform. Argal, she drowned herself wittingly.

c. 1599–1602 (date written), William Shakespeare, “The Tragedie of Hamlet, Prince of Denmarke”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act V, scene i], lines 11-13

He thought: 900 pesos=100 bottles of whiskey=900 ditto tequila. Argal: one should drink neither tequila nor whiskey but mescal.

1947, Malcolm Lowry, Under the Volcano, New York: Reynal & Hitchcock, page 77