It is simply a translation of Fr. main de gloire. But the French expression is a popular corruption of mandragore, from Lat. mandragora, the mandragore, or mandrake, to the forked roots of which a similar virtue was attributed, especially if the plant were obtained from the foot of the gallows.
CONTAMINATION
Akin to folk-etymology is contamination, i.e., the welding of two words into one. This can often be noticed in children, whose linguistic instincts are those of primitive races. I have heard a child, on her first visit to the Zoo, express great eagerness to see the canimals (camels × animals), which, by the way, turned out to be the giraffes. A small boy who learnt English and German simultaneously evolved, at the age of two, the word spam (sponge × Ger. Schwamm). In a college in the English midlands, a student named Constantine, who sat next to a student named Turpin, once heard himself startlingly addressed by a lecturer as Turpentine. People who inhabit the frontier of two languages, and in fact all who are in any degree bilingual, must inevitably form such composites occasionally. The h aspirate of Fr. haut, Lat. altus, high, can only be explained by the influence of Old High Ger. hōh (hoch). The poetic word glaive cannot be derived from Lat. gladius, sword, which has given Fr. glai, an archaic name for the gladiolus. We must invoke the help of a Gaulish word cladebo, sword, which is related to Gaelic clay-more, big sword. It has been said that in this word the swords of Cæsar and Vercingetorix still cross each other. In Old French we find oreste, a storm, combined from orage and tempeste (tempête). Fr. orteil, toe, represents the mixture of Lat. articulus, a little joint, with Gaulish ordag. A battledore was in Mid. English a washing beetle, which is in Provençal batedor, lit. beater. Hence it seems that this is one of the very few Provençal words which passed directly into English during the period of our occupation of Guienne. It has been contaminated by the cognate beetle.
Cannibal is from Span. canibal, earlier caribal, i.e. Carib, the n being perhaps due to contamination with Span. canino, canine, voracious. It can hardly be doubted that this word suggested Shakespeare's Caliban. Seraglio is due to confusion between the Turkish word serai, a palace, and Ital. serraglio, "an inclosure, a close, a padocke, a parke, a cloister or secluse" (Florio), which belongs to Lat. sera, a bolt or bar.
Anecdotage is a deliberate coinage ascribed to John Wilkes—
"When a man fell into his anecdotage, it was a sign for him to retire from the world."
(Disraeli, Lothair, Ch. 28.)
ARBOUR—FRET
In some cases it is impossible to estimate the different elements in a word. Arbour certainly owes its modern spelling to Lat. arbor, a tree, but it represents also Mid. Eng. herbere, erbere, which comes, through French, from Lat. *herbarium. But this can only mean herb-garden, so that the sense development of the word must have been affected by harbour, properly "army-shelter," ultimately identical with Fr. auberge (p. [164]). When Dryden wrote—
"Tardy of aid, unseal thy heavy eyes,
Awake, and with the dawning day arise."