This tango by Carlos Gardel is perhaps best known for its inclusion in the films “True Lies” and “Scent of a Woman.” I speak a little Spanish, but assume that the translation is a little more idiomatic/pleasant than “For the Head.” What say you?
I cannot speak definitively, but, I do know that in spanish one doesn’t say my body part, or your body part, but the body part. Duele la cabeza translates to my head hurts.
I’m not sure if it makes any difference to a song title (and I’m not a Spanish scholar,) but I think “una” means “one,” and “un” means “a.” So, the title means “For One Head.” That’s pretty mysterious either way.
no, uno means one, un/a is masculine/feminine
which makes me think the title probably means for her head, or for a ladies head
No, “una” is used because the noun, cabeza, is feminine. As for the meaning of the phrase, my knowledge of Spanish does not extend much into idioms, so I have no clue. 
It means “By a head”, as in the amount by which a horserace was lost.
Here are the original Spanish lyrics with English translation (the title is given as “By the head of a horse”, but of course “una cabeza” doesn’t imply a horse’s head per se, but only in the context of the song.
outlierrn, “cabeza” is feminine, so it’s always “una cabeza”, never “uno cabeza”; you can’t tell if it’s the head of a male or a female (or a horse!)from the article.
In Spanish, the word “por” can mean for, by, by means of, during, or through, depending upon context.
Thanks, everybody! Good responses, and very helpful. The best recording I’ve found of the song is by the Tango Project, BTW, as the “True Lies” soundtrack doesn’t include it.
Adios.
“For”, as in “intended for”, would be para, not por. Por almost always translates to English as “by”.
It is true that Spanish makes much less frequent use of the possessive than English does in cases like this.
But, when describing one’s own body, it is usual to add a reflexive pronoun in order to make clear that you are speaking about yourself.
So, “My head hurts” would be best said “Me duele la cabeza.”
OOOK!, cracks knuckles, Gardel´s hommie coming through, make way please… =)
The song in particular speaks of the misfortunes of a horse race gambler in love, it draws a parallel on how he looses time and time again in both love and the races and how he knows he´ll fall for gambling and women again.
In particular, the line “Por una cabeza de un noble potrillo”, refers to the finishing of a race, where a horse wins by just a heads lenght lead; a “potrillo” is a young male horse, “potranca” is the femenine.
This song doesn´t show too much Lunfardo (a dialect from the River Plate area, mostly Buenos Aires and Montevideo that borrows words and expressions from several languages and many unique to the region), compared to most other tangos, some are very criptic if you don´t have a good knowledge of the slang.
The only Lunfardo words I see here are “Metejón de un día” (a one day love affair), “Timba” (gambling, my grandmother was a great timbera 
) and Pingo (Horse)
Here´s a link to a dictionary containing lots of Lunfardo words and expressions.
P.S: both tango sequences in True Lies and Scent of a Woman are funny as hell for the local audience (specially the first), try to imagine a gaucho dancing Hip-hop and you´ll get the idea. 