This is from my Oxford English Dictionary (English being more relevant to older words, seeing as the ancient English invented the language some centuries before the first anglo-american settlers bastardised it):
san*guine
–adjective
1. cheerfully optimistic, hopeful, or confident: a sanguine disposition; sanguine expectations.
2. reddish; ruddy: a sanguine complexion.
3. (in old physiology) having blood as the predominating humor and consequently being ruddy-faced, cheerful, etc.
4. bloody; sanguinary.
5. blood-red; red.
6. Heraldry. a reddish-purple tincture.
–noun
7. a red iron-oxide crayon used in making drawings.
-Modern usage
1.
a. Of the color of blood; red.
b. Of a healthy reddish color; ruddy
-archaic
2. Archaic
a. Having blood as the dominant humor in terms of medieval physiology.
b. Having the temperament and ruddy complexion formerly thought to be characteristic of a person dominated by this humor; passionate.
-consolidate
3. Cheerfully confident; optimistic.
Related forms:
san⋅guine⋅ly, adverb
san⋅guin⋅i⋅ty, san⋅guin⋅ness, noun
Synonyms:
1. enthusiastic, buoyant, animated, lively, spirited.
Antonyms:
1. morose.
Anyway, interms of the blood/sanguine bit, it breaks down like this:
Sanguine is of the colour of blood, or relative to blood.
Bloody - is sanguinary.
Bloodthirsty - would be to diplay or have sanguinity or be sanguineous.
Sanguine is even in its most archaic form still meaning cheerful - sanguinary bloodthirsty. Yes, sang means blood in french and sanguis is latin for blood. However, the medieval mind broke down the visible temperament by color relating to bodily fluids (bile, phlegm, blood,black bile) - and the color then determined the predominant aspects to which a person behaved. If blood was the overall colour (sang) than a person was generally cheerful and happy. If this is not the archaic understanding you imagine having anything remotely linked to modern usage - think about 'his mood is black' or 'tickled pink' (pink is a lighter red). Further to this it can also refer to the flushed or blushing complexion when 'blood' was considered to fill the skin. You are wrong to think it means otherwise, so is your dictionary - but that's what this thread is all about.