Mrs. O'Flaherty: ... Theres [sic] lots thought she was going to marry young Master Lawless—
Sir Pearce: What! That—that—that bosthoon!
Mrs. O'Flaherty: [hilariously] Let your honor alone for finding the right word! A big bosthoon he is indeed, your honor."
—George Bernard Shaw, O'Flaherty V.C., 1919
In Irish Gaelic, a bastūn is literally a whip made of green rushes. Imagine trying to hurt someone with a bundle of leaves, and you'll see why the Gaelic bastūn also came to refer to a weak or spiritless person. It was this meaning that followed bastūn into English, where it became bosthoon, a word that means "boor" or "dolt." The Gaelic word, in turn, comes ultimately from the Late Latin word bastum via medieval French.