Entry in progress—B.P.
     
Wikipedia: Straight up (bartending)
In bartending, the term straight up (or up) refers to an alcoholic drink that is shaken or stirred with ice and then strained and served without ice in a stemmed glass.
 
This is contrasted with a drink served neat – a single, unmixed liquor served without being cooled and without any water, ice, or other mixer. Neat drinks and rocks drinks are often served in a rocks glass but may be served in a shot glass or a cocktail glass.
 
Definitions and usage
There is some confusion in the usage of neat, straight up, straight, and up. All of these mean “served without ice,” but some bar patrons and some bartenders use them inconsistently.
 
“Neat” and “up” are relatively unambiguous, meaning respectively “a single, unmixed liquor” and “chilled and served without ice in a cocktail glass.” “Straight” is often used interchangeably with “neat” (in the United Kingdom and the United States), but it may mean “straight up” (as defined above).
 
“Straight up” means “chilled and served without ice in a cocktail glass” but is often used to mean “neat.”
 
“On the rocks” refers to liquor poured over ice cubes.
 
Wiktionary: straight up
Adverb
straight up (not comparable)
1.truthfully, honestly. seriously
She told me straight up that she did not want to go.
2.(of an alcoholic drink) chilled (stirred or shaken over ice) and served in a cocktail glass, with no ice
Gimmie a margarita, straight up.
Usage notes
There is significant confusion in the use of straight up and other terms in common bartending use – see neat: usage notes.
   
(Oxford English Dictionary)
straight, adj., n., and adv.
Unmixed, undiluted; of spirits, ‘neat’.
1874 Hotten’s Slang Dict. (rev. ed.) 312   Straight, an American phrase peculiar to dram-drinkers; similar to our word neat.
1879 A. W. Tourgée Fool’s Errand vii. 28,  I allers did like my liquor clar,—clar an’ straight.
1901 W. Churchill Crisis viii. 432   Stephen had never learned to like straight whiskey.
1934 J. O’Hara Appointment in Samarra (1935) vi. 171   You want ginger ale with yours, or straight?
 
straight-up n. U.S., unmixed, undiluted (cf. sense A. 9a).
1975 B. Garfield Death Sentence (1976) v. 30   He‥beckoned the barmaid. ‘Dewar’s straight up, darlin’.’
 
31 December 1841, Kalamazoo (MI) Gazette, pg. 1:
The time “used to was” when a gentleman would step up to the bar and call for “whiskey straight.” Now the “ageny” is to require a glass of the “extract of corn per se.”—New Era. 
 
10 March 1853, New Orleaons (LA) Picayune, “A New Machine,” pg. 1:
Presently, as they stood at the counter taking some refreshment not wholly approved of by Father Mathew, the country gentleman, loosening his tongue under the influence of “whiskey straight,” began to communicate his private affairs and objects in visiting the city.
 
31 August 1857, Springfield (MA) Republican, pg. 2, col. 3:
Presently William Weir, Esq. appears with a cigar in his mouth, evidently under the influence of a whisky straight, all but the straight, for he is too fond of curvilinear lines in his movements.
   
27 October 1964, New York (NY) Times, “Food: On the Rocks at Cocktail Time” by Craig Claiborne, pg. 32:
THE drinking habits of New Yorkers change from restaurant to restaurant, season to season and midday to evening. Their favorite drinks are martinis and Scotch, drunk, more often than not, over ice, or to use the popular phrase “on the rocks,” although less than 10 years ago the thought of drinking cocktails in such a fashion was all but unheard of.
     
One of the three most popular noontime drinks is the bloody Mary, and it is generally served “straight up”—the term that designates the absence of ice.
   
OCLC WorldCat record 
Straight up or on the rocks : the story of the American cocktail
Author: William Grimes
Publisher: New York : North Point Press, 2001.
Edition/Format:  Book : English