Etymology
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head over heels (adv.)
1726, "a curious perversion" [Weekley] of Middle English heels over head (late 14c.) "somersault fashion," hence "recklessly." Head (n.) and heels long have been paired in alliterative phrases in English, and the whole image also was in classical Latin (per caput pedesque ire).
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head shop (n.)
emporium for stoner gear, by 1969 (noted in 1966 as the name of a specific shop in New York City selling psychedelic stuff), from head (n.) in the drug sense.
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Sieg Heil (interj.)
Nazi salute, German, literally "hail victory;" from German Sieg "victory," from Old High German sigu (see Siegfried) + heil "to hail," from Proto-Germanic *hailitho (see health). English heil was used in Middle English as a salutation implying respect or reverence (c. 1200; see hail (interj.)).
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Anno Hegirae 
Medieval Latin, "in the year of the hegira," the flight of Muhammad from Mecca, 622 C.E., from which Muslims reckon time; from ablative of annus "year" (see annual (adj.)) + genitive of hegira. Abbreviated A.H.
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red herring (n.)

"smoked herring" early 15c. (they turn red when cured), as opposed to white herring "fresh herring." Supposedly used by fugitives to put bloodhounds off their scent (1680s), hence metaphoric sense (1864) of "something used to divert attention from the basic issue;" earlier it simply meant "a false lead":

Though I have not the honour of being one of those sagacious country gentlemen, who have so long vociferated for the American war, who have so long run on the red-herring scent of American taxation before they found out there was no game on foot; (etc.) [Parliamentary speech dated March 20, 1782, reprinted in "Beauties of the British Senate," London, 1786]
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bleeding heart (n.)
name applied to several types of flowering plant, 1690s; see bleeding (adj.) + heart (n.).

In the sense of "person liberally and excessively sympathetic" (especially toward those the speaker or writer deems not to deserve it) is attested by 1951, but said by many to have been popularized with reference to liberals (especially Eleanor Roosevelt) in 1930s by newspaper columnist Westbrook Pegler (1894-1969), though quotations are wanting; bleeding in a figurative sense of "generous" is from late 16c., and the notion of one's heart bleeding as a figure of emotional anguish is from late 14c.; the exact image here may be the "bleeding heart of Jesus."
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ipso facto 
Latin adverbial phrase, literally "by that very fact, by the fact itself," from neuter ablative of ipse "he, himself, self" + ablative of factum "fact" (see fact).
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Montezuma 

name borne by two rulers of Tenochtitlan in ancient Mesoamerica, from Spanish Moctezuma, from Nahuatl (Aztecan) Moteuczoma, said to mean "he who frowns like a lord" or "he who is angry in a noble manner." Montezuma's revenge, "severe intestinal infection" sometimes suffered by non-natives in Mexico, is by 1962, in reference to Montezuma II (1466-1520), Aztec ruler at the time of the Spanish arrival and conquest of Mexico.

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fifth column (n.)
1936, from Gen. Emilio Mola's comment at the siege of Madrid during the Spanish Civil War that he would take the city with his four columns of troops outside it and his "fifth column" (quinta columna) in the city.
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white feather (n.)
as a symbol of cowardice, 1785, said to be from the time when cock-fighting was respectable, and when the strain of game-cock in vogue had no white feathers, so that "having a white feather, is proof he is not of the true game breed" [Grose].
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